disposable.patch

diff --git a/MimeKit/AttachmentCollection.cs b/MimeKit/AttachmentCollection.cs
index 30e0b93..5303fa5 100644
--- a/MimeKit/AttachmentCollection.cs
+++ b/MimeKit/AttachmentCollection.cs
@@ -472,6 +472,9 @@ namespace MimeKit {
 		/// </remarks>
 		public void Clear ()
 		{
+			for (int i = 0; i < attachments.Count; i++)
+				attachments[i].Dispose ();
+
 			attachments.Clear ();
 		}
 
@@ -599,6 +602,7 @@ namespace MimeKit {
 			if (index < 0 || index > Count)
 				throw new ArgumentOutOfRangeException ("index");
 
+			attachments[index].Dispose ();
 			attachments.RemoveAt (index);
 		}
 
diff --git a/MimeKit/ContentObject.cs b/MimeKit/ContentObject.cs
index 936e059..d8c32b1 100644
--- a/MimeKit/ContentObject.cs
+++ b/MimeKit/ContentObject.cs
@@ -41,7 +41,7 @@ namespace MimeKit {
 	/// </remarks>
 	public class ContentObject : IContentObject
 	{
-		readonly Stream content;
+		Stream content;
 
 		/// <summary>
 		/// Initializes a new instance of the <see cref="MimeKit.ContentObject"/> class.
@@ -76,7 +76,24 @@ namespace MimeKit {
 			content = stream;
 		}
 
-		#region IContentObject implementation
+		/// <summary>
+		/// Releases unmanaged resources and performs other cleanup operations before the
+		/// <see cref="MimeKit.ContentObject"/> is reclaimed by garbage collection.
+		/// </summary>
+		/// <remarks>
+		/// Releases unmanaged resources and performs other cleanup operations before the
+		/// <see cref="MimeKit.ContentObject"/> is reclaimed by garbage collection.
+		/// </remarks>
+		~ContentObject ()
+		{
+			Dispose (false);
+		}
+
+		void CheckDisposed ()
+		{
+			if (content == null)
+				throw new ObjectDisposedException ("ContentObject");
+		}
 
 		/// <summary>
 		/// Gets or sets the content encoding.
@@ -99,8 +116,13 @@ namespace MimeKit {
 		/// stream using <see cref="DecodeTo(System.IO.Stream,System.Threading.CancellationToken)"/>.
 		/// </remarks>
 		/// <returns>The decoded content stream.</returns>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The <see cref="ContentObject"/> has been disposed.
+		/// </exception>
 		public Stream Open ()
 		{
+			CheckDisposed ();
+
 			content.Seek (0, SeekOrigin.Begin);
 
 			var filtered = new FilteredStream (content);
@@ -122,6 +144,9 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="stream"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The <see cref="ContentObject"/> has been disposed.
+		/// </exception>
 		/// <exception cref="System.OperationCanceledException">
 		/// The operation was canceled via the cancellation token.
 		/// </exception>
@@ -133,6 +158,8 @@ namespace MimeKit {
 			if (stream == null)
 				throw new ArgumentNullException ("stream");
 
+			CheckDisposed ();
+
 			var readable = content as ICancellableStream;
 			var writable = stream as ICancellableStream;
 			var buf = new byte[4096];
@@ -182,6 +209,9 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="stream"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The <see cref="ContentObject"/> has been disposed.
+		/// </exception>
 		/// <exception cref="System.OperationCanceledException">
 		/// The operation was canceled via the cancellation token.
 		/// </exception>
@@ -193,6 +223,8 @@ namespace MimeKit {
 			if (stream == null)
 				throw new ArgumentNullException ("stream");
 
+			CheckDisposed ();
+
 			using (var filtered = new FilteredStream (stream)) {
 				filtered.Add (DecoderFilter.Create (Encoding));
 				WriteTo (filtered, cancellationToken);
@@ -200,6 +232,35 @@ namespace MimeKit {
 			}
 		}
 
-		#endregion
+		/// <summary>
+		/// Releases the unmanaged resources used by the <see cref="ContentObject"/> and
+		/// optionally releases the managed resources.
+		/// </summary>
+		/// <remarks>
+		/// Releases the unmanaged resources used by the <see cref="ContentObject"/> and
+		/// optionally releases the managed resources.
+		/// </remarks>
+		/// <param name="disposing"><c>true</c> to release both managed and unmanaged resources;
+		/// <c>false</c> to release only the unmanaged resources.</param>
+		protected virtual void Dispose (bool disposing)
+		{
+			if (disposing && content != null) {
+				content.Dispose ();
+				content = null;
+			}
+		}
+
+		/// <summary>
+		/// Releases all resources used by the <see cref="MimeKit.ContentObject"/> object.
+		/// </summary>
+		/// <remarks>Call <see cref="Dispose()"/> when you are finished using the <see cref="MimeKit.ContentObject"/>. The
+		/// <see cref="Dispose()"/> method leaves the <see cref="MimeKit.ContentObject"/> in an unusable state. After
+		/// calling <see cref="Dispose()"/>, you must release all references to the <see cref="MimeKit.ContentObject"/> so
+		/// the garbage collector can reclaim the memory that the <see cref="MimeKit.ContentObject"/> was occupying.</remarks>
+		public void Dispose ()
+		{
+			Dispose (true);
+			GC.SuppressFinalize (this);
+		}
 	}
 }
diff --git a/MimeKit/Cryptography/ApplicationPgpEncrypted.cs b/MimeKit/Cryptography/ApplicationPgpEncrypted.cs
index 29c8605..9dfcd98 100644
--- a/MimeKit/Cryptography/ApplicationPgpEncrypted.cs
+++ b/MimeKit/Cryptography/ApplicationPgpEncrypted.cs
@@ -71,6 +71,12 @@ namespace MimeKit.Cryptography {
 			ContentObject = new ContentObject (content);
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("ApplicationPgpEncrypted");
+		}
+
 		/// <summary>
 		/// Dispatches to the specific visit method for this MIME entity.
 		/// </summary>
@@ -86,11 +92,16 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitApplicationPgpEncrypted (this);
 		}
 	}
diff --git a/MimeKit/Cryptography/ApplicationPgpSignature.cs b/MimeKit/Cryptography/ApplicationPgpSignature.cs
index ea81d0f..5a00f39 100644
--- a/MimeKit/Cryptography/ApplicationPgpSignature.cs
+++ b/MimeKit/Cryptography/ApplicationPgpSignature.cs
@@ -78,6 +78,12 @@ namespace MimeKit.Cryptography {
 			ContentObject = new ContentObject (stream);
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("ApplicationPgpSignature");
+		}
+
 		/// <summary>
 		/// Dispatches to the specific visit method for this MIME entity.
 		/// </summary>
@@ -93,11 +99,16 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitApplicationPgpSignature (this);
 		}
 	}
diff --git a/MimeKit/Cryptography/ApplicationPkcs7Mime.cs b/MimeKit/Cryptography/ApplicationPkcs7Mime.cs
index c5efaef..99f1dba 100644
--- a/MimeKit/Cryptography/ApplicationPkcs7Mime.cs
+++ b/MimeKit/Cryptography/ApplicationPkcs7Mime.cs
@@ -111,6 +111,12 @@ namespace MimeKit.Cryptography {
 			}
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("ApplicationPkcs7Mime");
+		}
+
 		/// <summary>
 		/// Gets the value of the "smime-type" parameter.
 		/// </summary>
@@ -150,11 +156,16 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitApplicationPkcs7Mime (this);
 		}
 
@@ -169,6 +180,9 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="ctx"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.InvalidOperationException">
 		/// The "smime-type" parameter on the Content-Type header is not "compressed-data".
 		/// </exception>
@@ -180,6 +194,8 @@ namespace MimeKit.Cryptography {
 			if (ctx == null)
 				throw new ArgumentNullException ("ctx");
 
+			CheckDisposed ();
+
 			if (SecureMimeType != SecureMimeType.CompressedData)
 				throw new InvalidOperationException ();
 
@@ -198,6 +214,9 @@ namespace MimeKit.Cryptography {
 		/// Decompresses the content using the default <see cref="SecureMimeContext"/>.
 		/// </remarks>
 		/// <returns>The decompressed <see cref="MimeKit.MimeEntity"/>.</returns>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.InvalidOperationException">
 		/// The "smime-type" parameter on the Content-Type header is not "compressed-data".
 		/// </exception>
@@ -225,6 +244,9 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="ctx"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.InvalidOperationException">
 		/// The "smime-type" parameter on the Content-Type header is not "enveloped-data".
 		/// </exception>
@@ -236,6 +258,8 @@ namespace MimeKit.Cryptography {
 			if (ctx == null)
 				throw new ArgumentNullException ("ctx");
 
+			CheckDisposed ();
+
 			if (SecureMimeType != SecureMimeType.EnvelopedData)
 				throw new InvalidOperationException ();
 
@@ -254,6 +278,9 @@ namespace MimeKit.Cryptography {
 		/// Decrypts the content using the default <see cref="SecureMimeContext"/>.
 		/// </remarks>
 		/// <returns>The decrypted <see cref="MimeKit.MimeEntity"/>.</returns>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.InvalidOperationException">
 		/// The "smime-type" parameter on the Content-Type header is not "certs-only".
 		/// </exception>
@@ -277,6 +304,9 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="ctx"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.InvalidOperationException">
 		/// The "smime-type" parameter on the Content-Type header is not "certs-only".
 		/// </exception>
@@ -288,6 +318,8 @@ namespace MimeKit.Cryptography {
 			if (ctx == null)
 				throw new ArgumentNullException ("ctx");
 
+			CheckDisposed ();
+
 			if (SecureMimeType != SecureMimeType.CertsOnly)
 				throw new InvalidOperationException ();
 
@@ -311,6 +343,9 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="ctx"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.InvalidOperationException">
 		/// The "smime-type" parameter on the Content-Type header is not "signed-data".
 		/// </exception>
@@ -322,6 +357,8 @@ namespace MimeKit.Cryptography {
 			if (ctx == null)
 				throw new ArgumentNullException ("ctx");
 
+			CheckDisposed ();
+
 			if (SecureMimeType != SecureMimeType.SignedData)
 				throw new InvalidOperationException ();
 
@@ -341,6 +378,9 @@ namespace MimeKit.Cryptography {
 		/// </remarks>
 		/// <returns>The list of digital signatures.</returns>
 		/// <param name="entity">The unencapsulated entity.</param>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.InvalidOperationException">
 		/// The "smime-type" parameter on the Content-Type header is not "signed-data".
 		/// </exception>
diff --git a/MimeKit/Cryptography/ApplicationPkcs7Signature.cs b/MimeKit/Cryptography/ApplicationPkcs7Signature.cs
index d721ee0..eb46450 100644
--- a/MimeKit/Cryptography/ApplicationPkcs7Signature.cs
+++ b/MimeKit/Cryptography/ApplicationPkcs7Signature.cs
@@ -92,11 +92,17 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			if (IsDisposed)
+				throw new ObjectDisposedException ("ApplicationPkcs7Signature");
+
 			visitor.VisitApplicationPkcs7Signature (this);
 		}
 	}
diff --git a/MimeKit/Cryptography/MultipartEncrypted.cs b/MimeKit/Cryptography/MultipartEncrypted.cs
index dde049a..c7e7025 100644
--- a/MimeKit/Cryptography/MultipartEncrypted.cs
+++ b/MimeKit/Cryptography/MultipartEncrypted.cs
@@ -65,6 +65,12 @@ namespace MimeKit.Cryptography {
 		{
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("MultipartEncrypted");
+		}
+
 		/// <summary>
 		/// Dispatches to the specific visit method for this MIME entity.
 		/// </summary>
@@ -80,11 +86,16 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitMultipartEncrypted (this);
 		}
 
@@ -607,8 +618,13 @@ namespace MimeKit.Cryptography {
 				// add the protocol version part
 				encrypted.Add (new ApplicationPgpEncrypted ());
 
-				// add the encrypted entity as the second part
-				encrypted.Add (ctx.SignAndEncrypt (signer, digestAlgo, recipients, memory));
+				try {
+					// add the encrypted entity as the second part
+					encrypted.Add (ctx.SignAndEncrypt (signer, digestAlgo, recipients, memory));
+				} catch {
+					encrypted.Dispose ();
+					throw;
+				}
 
 				return encrypted;
 			}
@@ -737,8 +753,13 @@ namespace MimeKit.Cryptography {
 				// add the protocol version part
 				encrypted.Add (new ApplicationPgpEncrypted ());
 
-				// add the encrypted entity as the second part
-				encrypted.Add (ctx.SignAndEncrypt (signer, digestAlgo, cipherAlgo, recipients, memory));
+				try {
+					// add the encrypted entity as the second part
+					encrypted.Add (ctx.SignAndEncrypt (signer, digestAlgo, cipherAlgo, recipients, memory));
+				} catch {
+					encrypted.Dispose ();
+					throw;
+				}
 
 				return encrypted;
 			}
@@ -813,8 +834,13 @@ namespace MimeKit.Cryptography {
 				// add the protocol version part
 				encrypted.Add (new ApplicationPgpEncrypted ());
 
-				// add the encrypted entity as the second part
-				encrypted.Add (ctx.SignAndEncrypt (signer, digestAlgo, recipients, memory));
+				try {
+					// add the encrypted entity as the second part
+					encrypted.Add (ctx.SignAndEncrypt (signer, digestAlgo, recipients, memory));
+				} catch {
+					encrypted.Dispose ();
+					throw;
+				}
 
 				return encrypted;
 			}
@@ -986,8 +1012,13 @@ namespace MimeKit.Cryptography {
 				// add the protocol version part
 				encrypted.Add (new ApplicationPgpEncrypted ());
 
-				// add the encrypted entity as the second part
-				encrypted.Add (ctx.Encrypt (recipients, memory));
+				try {
+					// add the encrypted entity as the second part
+					encrypted.Add (ctx.Encrypt (recipients, memory));
+				} catch {
+					encrypted.Dispose ();
+					throw;
+				}
 
 				return encrypted;
 			}
@@ -1081,8 +1112,13 @@ namespace MimeKit.Cryptography {
 				// add the protocol version part
 				encrypted.Add (new ApplicationPgpEncrypted ());
 
-				// add the encrypted entity as the second part
-				encrypted.Add (ctx.Encrypt (algorithm, recipients, memory));
+				try {
+					// add the encrypted entity as the second part
+					encrypted.Add (ctx.Encrypt (algorithm, recipients, memory));
+				} catch {
+					encrypted.Dispose ();
+					throw;
+				}
 
 				return encrypted;
 			}
@@ -1137,8 +1173,13 @@ namespace MimeKit.Cryptography {
 				// add the protocol version part
 				encrypted.Add (new ApplicationPgpEncrypted ());
 
-				// add the encrypted entity as the second part
-				encrypted.Add (ctx.Encrypt (recipients, memory));
+				try {
+					// add the encrypted entity as the second part
+					encrypted.Add (ctx.Encrypt (recipients, memory));
+				} catch {
+					encrypted.Dispose ();
+					throw;
+				}
 
 				return encrypted;
 			}
@@ -1230,6 +1271,9 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="ctx"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.FormatException">
 		/// <para>The <c>protocol</c> parameter was not specified.</para>
 		/// <para>-or-</para>
@@ -1252,6 +1296,8 @@ namespace MimeKit.Cryptography {
 			if (ctx == null)
 				throw new ArgumentNullException ("ctx");
 
+			CheckDisposed ();
+
 			var protocol = ContentType.Parameters["protocol"];
 			if (string.IsNullOrEmpty (protocol))
 				throw new FormatException ();
@@ -1298,6 +1344,9 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="ctx"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.FormatException">
 		/// <para>The <c>protocol</c> parameter was not specified.</para>
 		/// <para>-or-</para>
@@ -1331,6 +1380,9 @@ namespace MimeKit.Cryptography {
 		/// </remarks>
 		/// <returns>The decrypted entity.</returns>
 		/// <param name="signatures">A list of digital signatures if the data was both signed and encrypted.</param>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.FormatException">
 		/// <para>The <c>protocol</c> parameter was not specified.</para>
 		/// <para>-or-</para>
@@ -1351,6 +1403,8 @@ namespace MimeKit.Cryptography {
 		/// </exception>
 		public MimeEntity Decrypt (out DigitalSignatureCollection signatures)
 		{
+			CheckDisposed ();
+
 			var protocol = ContentType.Parameters["protocol"];
 			if (string.IsNullOrEmpty (protocol))
 				throw new FormatException ();
@@ -1400,6 +1454,9 @@ namespace MimeKit.Cryptography {
 		/// Decrypts the <see cref="MultipartEncrypted"/> part.
 		/// </remarks>
 		/// <returns>The decrypted entity.</returns>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.FormatException">
 		/// <para>The <c>protocol</c> parameter was not specified.</para>
 		/// <para>-or-</para>
diff --git a/MimeKit/Cryptography/MultipartSigned.cs b/MimeKit/Cryptography/MultipartSigned.cs
index 73c013d..7a43d4c 100644
--- a/MimeKit/Cryptography/MultipartSigned.cs
+++ b/MimeKit/Cryptography/MultipartSigned.cs
@@ -64,6 +64,12 @@ namespace MimeKit.Cryptography {
 		{
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("MultipartSigned");
+		}
+
 		/// <summary>
 		/// Dispatches to the specific visit method for this MIME entity.
 		/// </summary>
@@ -79,11 +85,16 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitMultipartSigned (this);
 		}
 
@@ -152,11 +163,20 @@ namespace MimeKit.Cryptography {
 				// Note: we need to parse the modified entity structure to preserve any modifications
 				var parser = new MimeParser (memory, MimeFormat.Entity);
 				var parsed = parser.ParseEntity ();
+				MimePart signature;
+
 				memory.Position = 0;
 
-				// sign the cleartext content
-				var signature = ctx.Sign (signer, digestAlgo, memory);
+				try {
+					// sign the cleartext content
+					signature = ctx.Sign (signer, digestAlgo, memory);
+				} catch {
+					parsed.Dispose ();
+					throw;
+				}
+
 				var micalg = ctx.GetDigestAlgorithmName (digestAlgo);
+
 				var signed = new MultipartSigned ();
 
 				// set the protocol and micalg Content-Type parameters
@@ -415,11 +435,16 @@ namespace MimeKit.Cryptography {
 		/// <para>-or-</para>
 		/// <para><paramref name="constraint"/> is not a valid value.</para>
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Prepare (EncodingConstraint constraint, int maxLineLength = 78)
 		{
 			if (maxLineLength < 72 || maxLineLength > 998)
 				throw new ArgumentOutOfRangeException ("maxLineLength");
 
+			CheckDisposed ();
+
 			// Note: we do not iterate over our children because they are already signed
 			// and changing them would break the signature. They should already be
 			// properly prepared, anyway.
@@ -436,6 +461,9 @@ namespace MimeKit.Cryptography {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="ctx"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.FormatException">
 		/// The multipart is malformed in some way.
 		/// </exception>
@@ -450,6 +478,8 @@ namespace MimeKit.Cryptography {
 			if (ctx == null)
 				throw new ArgumentNullException ("ctx");
 
+			CheckDisposed ();
+
 			var protocol = ContentType.Parameters["protocol"];
 			if (string.IsNullOrEmpty (protocol))
 				throw new FormatException ("The multipart/signed part did not specify a protocol.");
@@ -493,6 +523,9 @@ namespace MimeKit.Cryptography {
 		/// Verifies the multipart/signed part using the default cryptography context.
 		/// </remarks>
 		/// <returns>A signer info collection.</returns>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.FormatException">
 		/// <para>The <c>protocol</c> parameter was not specified.</para>
 		/// <para>-or-</para>
@@ -506,6 +539,8 @@ namespace MimeKit.Cryptography {
 		/// </exception>
 		public DigitalSignatureCollection Verify ()
 		{
+			CheckDisposed ();
+
 			var protocol = ContentType.Parameters["protocol"];
 			if (string.IsNullOrEmpty (protocol))
 				throw new FormatException ("The multipart/signed part did not specify a protocol.");
diff --git a/MimeKit/IContentObject.cs b/MimeKit/IContentObject.cs
index 1203001..3b9f698 100644
--- a/MimeKit/IContentObject.cs
+++ b/MimeKit/IContentObject.cs
@@ -24,6 +24,7 @@
 // THE SOFTWARE.
 //
 
+using System;
 using System.IO;
 using System.Threading;
 
@@ -34,7 +35,7 @@ namespace MimeKit {
     /// <remarks>
     /// Implemented by <see cref="ContentObject"/>.
     /// </remarks>
-	public interface IContentObject
+	public interface IContentObject : IDisposable
 	{
 		/// <summary>
 		/// Gets the content encoding.
diff --git a/MimeKit/MessageDeliveryStatus.cs b/MimeKit/MessageDeliveryStatus.cs
index d3fbfae..800ec0a 100644
--- a/MimeKit/MessageDeliveryStatus.cs
+++ b/MimeKit/MessageDeliveryStatus.cs
@@ -64,6 +64,12 @@ namespace MimeKit {
 		{
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("MessageDeliveryStatus");
+		}
+
 		/// <summary>
 		/// Get the groups of delivery status fields.
 		/// </summary>
@@ -127,11 +133,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitMessageDeliveryStatus (this);
 		}
 	}
diff --git a/MimeKit/MessageDispositionNotification.cs b/MimeKit/MessageDispositionNotification.cs
index 193d5d8..2b5e343 100644
--- a/MimeKit/MessageDispositionNotification.cs
+++ b/MimeKit/MessageDispositionNotification.cs
@@ -65,6 +65,12 @@ namespace MimeKit {
 		{
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("MessageDispositionNotification");
+		}
+
 		/// <summary>
 		/// Get the disposition notification fields.
 		/// </summary>
@@ -117,11 +123,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitMessageDispositionNotification (this);
 		}
 	}
diff --git a/MimeKit/MessagePart.cs b/MimeKit/MessagePart.cs
index 9376b21..6bb743d 100644
--- a/MimeKit/MessagePart.cs
+++ b/MimeKit/MessagePart.cs
@@ -203,5 +203,23 @@ namespace MimeKit {
 			if (Message != null)
 				Message.WriteTo (options, stream, cancellationToken);
 		}
+
+		/// <summary>
+		/// Releases the unmanaged resources used by the <see cref="MessagePart"/> and
+		/// optionally releases the managed resources.
+		/// </summary>
+		/// <remarks>
+		/// Releases the unmanaged resources used by the <see cref="MessagePart"/> and
+		/// optionally releases the managed resources.
+		/// </remarks>
+		/// <param name="disposing"><c>true</c> to release both managed and unmanaged resources;
+		/// <c>false</c> to release only the unmanaged resources.</param>
+		protected override void Dispose (bool disposing)
+		{
+			if (disposing && !IsDisposed && Message != null)
+				Message.Dispose ();
+
+			base.Dispose (disposing);
+		}
 	}
 }
diff --git a/MimeKit/MessagePartial.cs b/MimeKit/MessagePartial.cs
index 4c04c45..9c89128 100644
--- a/MimeKit/MessagePartial.cs
+++ b/MimeKit/MessagePartial.cs
@@ -96,6 +96,12 @@ namespace MimeKit {
 			ContentType.Parameters.Add (new Parameter ("total", total.ToString ()));
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("MessagePartial");
+		}
+
 		/// <summary>
 		/// Gets the "id" parameter of the Content-Type header.
 		/// </summary>
@@ -165,6 +171,8 @@ namespace MimeKit {
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitMessagePartial (this);
 		}
 
diff --git a/MimeKit/MimeEntity.cs b/MimeKit/MimeEntity.cs
index b7d0a6c..fafd546 100644
--- a/MimeKit/MimeEntity.cs
+++ b/MimeKit/MimeEntity.cs
@@ -49,7 +49,7 @@ namespace MimeKit {
 	/// <see cref="MimePart"/> who's content is another MIME message/document). All other types are
 	/// derivatives of one of those.</para>
 	/// </remarks>
-	public abstract class MimeEntity
+	public abstract class MimeEntity : IDisposable
 	{
 		ContentDisposition disposition;
 		string contentId;
@@ -129,6 +129,25 @@ namespace MimeKit {
 		}
 
 		/// <summary>
+		/// Releases unmanaged resources and performs other cleanup operations before the
+		/// <see cref="MimeKit.MimeEntity"/> is reclaimed by garbage collection.
+		/// </summary>
+		/// <remarks>
+		/// Releases unmanaged resources and performs other cleanup operations before the
+		/// <see cref="MimeKit.MimeEntity"/> is reclaimed by garbage collection.
+		/// </remarks>
+		~MimeEntity ()
+		{
+			Dispose (false);
+		}
+
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("MimeEntity");
+		}
+
+		/// <summary>
 		/// Tries to use the given object to initialize the appropriate property.
 		/// </summary>
 		/// <remarks>
@@ -156,6 +175,17 @@ namespace MimeKit {
 		}
 
 		/// <summary>
+		/// Gets a value indicating whether the entity has been disposed.
+		/// </summary>
+		/// <remarks>
+		/// Gets a value indicating whether the entity has been disposed.
+		/// </remarks>
+		/// <value><c>true</c> if the entity has been disposed; otherwise, <c>false</c>.</value>
+		protected bool IsDisposed {
+			get; private set;
+		}
+
+		/// <summary>
 		/// Gets the list of headers.
 		/// </summary>
 		/// <remarks>
@@ -177,9 +207,14 @@ namespace MimeKit {
 		/// be <c>null</c>.
 		/// </remarks>
 		/// <value>The content disposition.</value>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public ContentDisposition ContentDisposition {
 			get { return disposition; }
 			set {
+				CheckDisposed ();
+
 				if (disposition == value)
 					return;
 
@@ -221,9 +256,14 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentException">
 		/// <paramref name="value"/> is not an absolute URI.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public Uri ContentBase {
 			get { return baseUri; }
 			set {
+				CheckDisposed ();
+
 				if (baseUri == value)
 					return;
 
@@ -252,9 +292,14 @@ namespace MimeKit {
 		/// <para>For more information, see http://www.ietf.org/rfc/rfc2110.txt</para>
 		/// </remarks>
 		/// <value>The content location or <c>null</c>.</value>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public Uri ContentLocation {
 			get { return location; }
 			set {
+				CheckDisposed ();
+
 				if (location == value)
 					return;
 
@@ -279,9 +324,14 @@ namespace MimeKit {
 		/// when the HTML-formatted message body needs to reference image attachments.</para>
 		/// </remarks>
 		/// <value>The content identifier.</value>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public string ContentId {
 			get { return contentId; }
 			set {
+				CheckDisposed ();
+
 				if (contentId == value)
 					return;
 
@@ -313,9 +363,14 @@ namespace MimeKit {
 		/// <see cref="MimePart"/> is not meant to be treated as an attachment.
 		/// </remarks>
 		/// <value><c>true</c> if this <see cref="MimePart"/> is an attachment; otherwise, <c>false</c>.</value>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public bool IsAttachment {
 			get { return ContentDisposition != null && ContentDisposition.IsAttachment; }
 			set {
+				CheckDisposed ();
+
 				if (value) {
 					if (ContentDisposition == null)
 						ContentDisposition = new ContentDisposition (ContentDisposition.Attachment);
@@ -334,8 +389,13 @@ namespace MimeKit {
 		/// Returns a <see cref="System.String"/> that represents the current <see cref="MimeKit.MimeEntity"/>.
 		/// </remarks>
 		/// <returns>A <see cref="System.String"/> that represents the current <see cref="MimeKit.MimeEntity"/>.</returns>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override string ToString ()
 		{
+			CheckDisposed ();
+
 			using (var memory = new MemoryStream ()) {
 				WriteTo (memory);
 
@@ -365,11 +425,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public virtual void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitMimeEntity (this);
 		}
 
@@ -386,6 +451,9 @@ namespace MimeKit {
 		/// <para>-or-</para>
 		/// <para><paramref name="constraint"/> is not a valid value.</para>
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public abstract void Prepare (EncodingConstraint constraint, int maxLineLength = 78);
 
 		/// <summary>
@@ -403,6 +471,9 @@ namespace MimeKit {
 		/// <para>-or-</para>
 		/// <para><paramref name="stream"/> is <c>null</c>.</para>
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.OperationCanceledException">
 		/// The operation was canceled via the cancellation token.
 		/// </exception>
@@ -417,6 +488,8 @@ namespace MimeKit {
 			if (stream == null)
 				throw new ArgumentNullException ("stream");
 
+			CheckDisposed ();
+
 			Headers.WriteTo (options, stream, cancellationToken);
 		}
 
@@ -706,6 +779,34 @@ namespace MimeKit {
 		}
 
 		/// <summary>
+		/// Releases the unmanaged resources used by the <see cref="MimeEntity"/> and
+		/// optionally releases the managed resources.
+		/// </summary>
+		/// <remarks>
+		/// Releases the unmanaged resources used by the <see cref="MimeEntity"/> and
+		/// optionally releases the managed resources.
+		/// </remarks>
+		/// <param name="disposing"><c>true</c> to release both managed and unmanaged resources;
+		/// <c>false</c> to release only the unmanaged resources.</param>
+		protected virtual void Dispose (bool disposing)
+		{
+		}
+
+		/// <summary>
+		/// Releases all resources used by the <see cref="MimeKit.MimeEntity"/> object.
+		/// </summary>
+		/// <remarks>Call <see cref="Dispose()"/> when you are finished using the <see cref="MimeKit.MimeEntity"/>. The
+		/// <see cref="Dispose()"/> method leaves the <see cref="MimeKit.MimeEntity"/> in an unusable state. After
+		/// calling <see cref="Dispose()"/>, you must release all references to the <see cref="MimeKit.MimeEntity"/> so
+		/// the garbage collector can reclaim the memory that the <see cref="MimeKit.MimeEntity"/> was occupying.</remarks>
+		public void Dispose ()
+		{
+			Dispose (true);
+			GC.SuppressFinalize (this);
+			IsDisposed = true;
+		}
+
+		/// <summary>
 		/// Load a <see cref="MimeEntity"/> from the specified stream.
 		/// </summary>
 		/// <remarks>
diff --git a/MimeKit/MimeMessage.cs b/MimeKit/MimeMessage.cs
index e1bfff6..e5cca89 100644
--- a/MimeKit/MimeMessage.cs
+++ b/MimeKit/MimeMessage.cs
@@ -62,7 +62,7 @@ namespace MimeKit {
 	/// tree of MIME entities such as a text/plain MIME part and a collection
 	/// of file attachments.</para>
 	/// </remarks>
-	public class MimeMessage
+	public class MimeMessage : IDisposable
 	{
 		static readonly string[] StandardAddressHeaders = {
 			"Resent-From", "Resent-Reply-To", "Resent-To", "Resent-Cc", "Resent-Bcc",
@@ -81,6 +81,7 @@ namespace MimeKit {
 		string messageId;
 		string inreplyto;
 		Version version;
+		bool disposed;
 
 		internal MimeMessage (ParserOptions options, IEnumerable<Header> headers)
 		{
@@ -239,6 +240,19 @@ namespace MimeKit {
 		}
 
 		/// <summary>
+		/// Releases unmanaged resources and performs other cleanup operations before the
+		/// <see cref="MimeKit.MimeMessage"/> is reclaimed by garbage collection.
+		/// </summary>
+		/// <remarks>
+		/// Releases unmanaged resources and performs other cleanup operations before the
+		/// <see cref="MimeKit.MimeMessage"/> is reclaimed by garbage collection.
+		/// </remarks>
+		~MimeMessage ()
+		{
+			Dispose (false);
+		}
+
+		/// <summary>
 		/// Gets the list of headers.
 		/// </summary>
 		/// <remarks>
@@ -2385,6 +2399,36 @@ namespace MimeKit {
 		}
 
 		/// <summary>
+		/// Releases the unmanaged resources used by the <see cref="MimeMessage"/> and
+		/// optionally releases the managed resources.
+		/// </summary>
+		/// <remarks>
+		/// Releases the unmanaged resources used by the <see cref="MimeMessage"/> and
+		/// optionally releases the managed resources.
+		/// </remarks>
+		/// <param name="disposing"><c>true</c> to release both managed and unmanaged resources;
+		/// <c>false</c> to release only the unmanaged resources.</param>
+		protected virtual void Dispose (bool disposing)
+		{
+			if (disposing && !disposed && Body != null)
+				Body.Dispose ();
+		}
+
+		/// <summary>
+		/// Releases all resources used by the <see cref="MimeKit.MimeMessage"/> object.
+		/// </summary>
+		/// <remarks>Call <see cref="Dispose()"/> when you are finished using the <see cref="MimeKit.MimeMessage"/>. The
+		/// <see cref="Dispose()"/> method leaves the <see cref="MimeKit.MimeMessage"/> in an unusable state. After
+		/// calling <see cref="Dispose()"/>, you must release all references to the <see cref="MimeKit.MimeMessage"/> so
+		/// the garbage collector can reclaim the memory that the <see cref="MimeKit.MimeMessage"/> was occupying.</remarks>
+		public void Dispose ()
+		{
+			Dispose (true);
+			GC.SuppressFinalize (this);
+			disposed = true;
+		}
+
+		/// <summary>
 		/// Load a <see cref="MimeMessage"/> from the specified stream.
 		/// </summary>
 		/// <remarks>
@@ -2616,14 +2660,20 @@ namespace MimeKit {
 		static MimePart GetMimePart (AttachmentBase item)
 		{
 			var mimeType = item.ContentType.ToString ();
-			var part = new MimePart (ContentType.Parse (mimeType));
+			var contentType = ContentType.Parse (mimeType);
+			ContentDisposition disposition = null;
 			var attachment = item as Attachment;
 
 			if (attachment != null) {
-				var disposition = attachment.ContentDisposition.ToString ();
-				part.ContentDisposition = ContentDisposition.Parse (disposition);
+				var text = attachment.ContentDisposition.ToString ();
+				disposition = ContentDisposition.Parse (text);
 			}
 
+			var part = new MimePart (contentType);
+
+			if (disposition != null)
+				part.ContentDisposition = disposition;
+
 			switch (item.TransferEncoding) {
 			case System.Net.Mime.TransferEncoding.QuotedPrintable:
 				part.ContentTransferEncoding = ContentEncoding.QuotedPrintable;
@@ -2636,8 +2686,12 @@ namespace MimeKit {
 				break;
 			}
 
-			if (item.ContentId != null)
-				part.ContentId = item.ContentId;
+			if (item.ContentId != null) {
+				try {
+					part.ContentId = item.ContentId;
+				} catch (ArgumentException) {
+				}
+			}
 
 			var stream = new MemoryBlockStream ();
 			item.ContentStream.CopyTo (stream);
@@ -2722,7 +2776,14 @@ namespace MimeKit {
 					alternative.Add (body);
 
 				foreach (var view in message.AlternateViews) {
-					var part = GetMimePart (view);
+					MimePart part;
+
+					try {
+						part = GetMimePart (view);
+					} catch {
+						alternative.Dispose ();
+						throw;
+					}
 
 					if (view.BaseUri != null)
 						part.ContentLocation = view.BaseUri;
@@ -2739,7 +2800,13 @@ namespace MimeKit {
 						related.Add (part);
 
 						foreach (var resource in view.LinkedResources) {
-							part = GetMimePart (resource);
+							try {
+								part = GetMimePart (resource);
+							} catch {
+								alternative.Dispose ();
+								related.Dispose ();
+								throw;
+							}
 
 							if (resource.ContentLink != null)
 								part.ContentLocation = resource.ContentLink;
@@ -2765,8 +2832,14 @@ namespace MimeKit {
 				if (body != null)
 					mixed.Add (body);
 
-				foreach (var attachment in message.Attachments)
-					mixed.Add (GetMimePart (attachment));
+				foreach (var attachment in message.Attachments) {
+					try {
+						mixed.Add (GetMimePart (attachment));
+					} catch {
+						mixed.Dispose ();
+						throw;
+					}
+				}
 
 				body = mixed;
 			}
diff --git a/MimeKit/MimePart.cs b/MimeKit/MimePart.cs
index e1b5de0..bdb9fca 100644
--- a/MimeKit/MimePart.cs
+++ b/MimeKit/MimePart.cs
@@ -100,36 +100,31 @@ namespace MimeKit {
 			if (args == null)
 				throw new ArgumentNullException ("args");
 
-			IContentObject content = null;
-
 			foreach (object obj in args) {
 				if (obj == null || TryInit (obj))
 					continue;
 
 				var co = obj as IContentObject;
 				if (co != null) {
-					if (content != null)
+					if (ContentObject != null)
 						throw new ArgumentException ("ContentObject should not be specified more than once.");
 
-					content = co;
+					ContentObject = co;
 					continue;
 				}
 
 				var stream = obj as Stream;
 				if (stream != null) {
-					if (content != null)
+					if (ContentObject != null)
 						throw new ArgumentException ("Stream (used as content) should not be specified more than once.");
 
 					// Use default as specified by ContentObject ctor when building a new MimePart.
-					content = new ContentObject (stream);
+					ContentObject = new ContentObject (stream);
 					continue;
 				}
 
 				throw new ArgumentException ("Unknown initialization parameter: " + obj.GetType ());
 			}
-
-			if (content != null)
-				ContentObject = content;
 		}
 
 		/// <summary>
@@ -194,6 +189,12 @@ namespace MimeKit {
 		{
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("MimePart");
+		}
+
 		/// <summary>
 		/// Gets or sets the duration of the content if available.
 		/// </summary>
@@ -336,11 +337,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitMimePart (this);
 		}
 
@@ -356,6 +362,9 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentOutOfRangeException">
 		/// <paramref name="constraint"/> is not a valid value.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.OperationCanceledException">
 		/// The operation was canceled via the cancellation token.
 		/// </exception>
@@ -382,6 +391,9 @@ namespace MimeKit {
 		/// <para>-or-</para>
 		/// <para><paramref name="constraint"/> is not a valid value.</para>
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.OperationCanceledException">
 		/// The operation was canceled via the cancellation token.
 		/// </exception>
@@ -390,6 +402,8 @@ namespace MimeKit {
 		/// </exception>
 		public ContentEncoding GetBestEncoding (EncodingConstraint constraint, int maxLineLength, CancellationToken cancellationToken = default (CancellationToken))
 		{
+			CheckDisposed ();
+
 			if (ContentObject == null)
 				return ContentEncoding.SevenBit;
 
@@ -417,8 +431,13 @@ namespace MimeKit {
 		/// <exception cref="System.InvalidOperationException">
 		/// The <see cref="ContentObject"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public string ComputeContentMd5 ()
 		{
+			CheckDisposed ();
+
 			if (ContentObject == null)
 				throw new InvalidOperationException ("Cannot compute Md5 checksum without a ContentObject.");
 
@@ -463,8 +482,13 @@ namespace MimeKit {
 		/// the values match.
 		/// </remarks>
 		/// <returns><c>true</c>, if content MD5 checksum was verified, <c>false</c> otherwise.</returns>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public bool VerifyContentMd5 ()
 		{
+			CheckDisposed ();
+
 			if (IsNullOrWhiteSpace (md5sum) || ContentObject == null)
 				return false;
 
@@ -496,11 +520,16 @@ namespace MimeKit {
 		/// <para>-or-</para>
 		/// <para><paramref name="constraint"/> is not a valid value.</para>
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Prepare (EncodingConstraint constraint, int maxLineLength = 78)
 		{
 			if (maxLineLength < 72 || maxLineLength > 998)
 				throw new ArgumentOutOfRangeException ("maxLineLength");
 
+			CheckDisposed ();
+
 			switch (ContentTransferEncoding) {
 			case ContentEncoding.QuotedPrintable:
 			case ContentEncoding.UUEncode:
@@ -537,6 +566,9 @@ namespace MimeKit {
 		/// <para>-or-</para>
 		/// <para><paramref name="stream"/> is <c>null</c>.</para>
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.OperationCanceledException">
 		/// The operation was canceled via the cancellation token.
 		/// </exception>
@@ -656,5 +688,23 @@ namespace MimeKit {
 				throw new ArgumentOutOfRangeException ("action");
 			}
 		}
+
+		/// <summary>
+		/// Releases the unmanaged resources used by the <see cref="MimePart"/> and
+		/// optionally releases the managed resources.
+		/// </summary>
+		/// <remarks>
+		/// Releases the unmanaged resources used by the <see cref="MimePart"/> and
+		/// optionally releases the managed resources.
+		/// </remarks>
+		/// <param name="disposing"><c>true</c> to release both managed and unmanaged resources;
+		/// <c>false</c> to release only the unmanaged resources.</param>
+		protected override void Dispose (bool disposing)
+		{
+			if (disposing && !IsDisposed && ContentObject != null)
+				ContentObject.Dispose ();
+
+			base.Dispose (disposing);
+		}
 	}
 }
diff --git a/MimeKit/Multipart.cs b/MimeKit/Multipart.cs
index f132fe4..bbbb840 100644
--- a/MimeKit/Multipart.cs
+++ b/MimeKit/Multipart.cs
@@ -145,6 +145,12 @@ namespace MimeKit {
 		{
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("Multipart");
+		}
+
 		static string GenerateBoundary ()
 		{
 			var base64 = new Base64Encoder (true);
@@ -169,12 +175,17 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="value"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public string Boundary {
 			get { return ContentType.Boundary; }
 			set {
 				if (value == null)
 					throw new ArgumentNullException ("value");
 
+				CheckDisposed ();
+
 				if (Boundary == value)
 					return;
 
@@ -197,6 +208,9 @@ namespace MimeKit {
 		/// it correctly.
 		/// </remarks>
 		/// <value>The preamble.</value>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public string Preamble {
 			get {
 				if (preamble == null && RawPreamble != null)
@@ -205,6 +219,8 @@ namespace MimeKit {
 				return preamble;
 			}
 			set {
+				CheckDisposed ();
+
 				if (preamble == value)
 					return;
 
@@ -231,6 +247,9 @@ namespace MimeKit {
 		/// child of the multipart and is rarely ever used.
 		/// </remarks>
 		/// <value>The epilogue.</value>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public string Epilogue {
 			get {
 				if (epilogue == null && RawEpilogue != null)
@@ -239,6 +258,8 @@ namespace MimeKit {
 				return epilogue;
 			}
 			set {
+				CheckDisposed ();
+
 				if (epilogue == value)
 					return;
 
@@ -268,11 +289,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitMultipart (this);
 		}
 
@@ -359,6 +385,8 @@ namespace MimeKit {
 			if (maxLineLength < 72 || maxLineLength > 998)
 				throw new ArgumentOutOfRangeException ("maxLineLength");
 
+			CheckDisposed ();
+
 			for (int i = 0; i < children.Count; i++)
 				children[i].Prepare (constraint, maxLineLength);
 		}
@@ -468,11 +496,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="part"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public void Add (MimeEntity part)
 		{
 			if (part == null)
 				throw new ArgumentNullException ("part");
 
+			CheckDisposed ();
+
 			children.Add (part);
 		}
 
@@ -482,8 +515,13 @@ namespace MimeKit {
 		/// <remarks>
 		/// Removes all of the parts within the multipart.
 		/// </remarks>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public void Clear ()
 		{
+			CheckDisposed ();
+
 			children.Clear ();
 		}
 
@@ -499,11 +537,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="part"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public bool Contains (MimeEntity part)
 		{
 			if (part == null)
 				throw new ArgumentNullException ("part");
 
+			CheckDisposed ();
+
 			return children.Contains (part);
 		}
 
@@ -522,8 +565,13 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentOutOfRangeException">
 		/// <paramref name="arrayIndex"/> is out of range.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public void CopyTo (MimeEntity[] array, int arrayIndex)
 		{
+			CheckDisposed ();
+
 			children.CopyTo (array, arrayIndex);
 		}
 
@@ -538,11 +586,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="part"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public bool Remove (MimeEntity part)
 		{
 			if (part == null)
 				throw new ArgumentNullException ("part");
 
+			CheckDisposed ();
+
 			return children.Remove (part);
 		}
 
@@ -561,11 +614,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="part"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public int IndexOf (MimeEntity part)
 		{
 			if (part == null)
 				throw new ArgumentNullException ("part");
 
+			CheckDisposed ();
+
 			return children.IndexOf (part);
 		}
 
@@ -583,6 +641,9 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentOutOfRangeException">
 		/// <paramref name="index"/> is out of range.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public void Insert (int index, MimeEntity part)
 		{
 			if (index < 0 || index > children.Count)
@@ -591,6 +652,8 @@ namespace MimeKit {
 			if (part == null)
 				throw new ArgumentNullException ("part");
 
+			CheckDisposed ();
+
 			children.Insert (index, part);
 		}
 
@@ -604,8 +667,17 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentOutOfRangeException">
 		/// <paramref name="index"/> is out of range.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public void RemoveAt (int index)
 		{
+			if (index < 0 || index > children.Count)
+				throw new ArgumentOutOfRangeException ("index");
+
+			CheckDisposed ();
+
+			children[index].Dispose ();
 			children.RemoveAt (index);
 		}
 
@@ -623,12 +695,24 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentOutOfRangeException">
 		/// <paramref name="index"/> is out of range.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public MimeEntity this[int index] {
 			get { return children[index]; }
 			set {
+				if (index < 0 || index > children.Count)
+					throw new ArgumentOutOfRangeException ("index");
+
 				if (value == null)
 					throw new ArgumentNullException ("value");
 
+				CheckDisposed ();
+
+				if (value == children[index])
+					return;
+
+				children[index].Dispose ();
 				children[index] = value;
 			}
 		}
@@ -644,8 +728,13 @@ namespace MimeKit {
 		/// Gets the enumerator for the children of the <see cref="Multipart"/>.
 		/// </remarks>
 		/// <returns>The enumerator.</returns>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public IEnumerator<MimeEntity> GetEnumerator ()
 		{
+			CheckDisposed ();
+
 			return children.GetEnumerator ();
 		}
 
@@ -660,11 +749,36 @@ namespace MimeKit {
 		/// Gets the enumerator for the children of the <see cref="Multipart"/>.
 		/// </remarks>
 		/// <returns>The enumerator.</returns>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		IEnumerator IEnumerable.GetEnumerator ()
 		{
+			CheckDisposed ();
+
 			return children.GetEnumerator ();
 		}
 
 		#endregion
+
+		/// <summary>
+		/// Releases the unmanaged resources used by the <see cref="Multipart"/> and
+		/// optionally releases the managed resources.
+		/// </summary>
+		/// <remarks>
+		/// Releases the unmanaged resources used by the <see cref="Multipart"/> and
+		/// optionally releases the managed resources.
+		/// </remarks>
+		/// <param name="disposing"><c>true</c> to release both managed and unmanaged resources;
+		/// <c>false</c> to release only the unmanaged resources.</param>
+		protected override void Dispose (bool disposing)
+		{
+			if (disposing && !IsDisposed) {
+				for (int i = 0; i < children.Count; i++)
+					children[i].Dispose ();
+			}
+
+			base.Dispose (disposing);
+		}
 	}
 }
diff --git a/MimeKit/MultipartAlternative.cs b/MimeKit/MultipartAlternative.cs
index 15cc761..15e8f00 100644
--- a/MimeKit/MultipartAlternative.cs
+++ b/MimeKit/MultipartAlternative.cs
@@ -82,6 +82,12 @@ namespace MimeKit {
 		{
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("MultipartAlternative");
+		}
+
 		/// <summary>
 		/// Get the text of the text/plain alternative.
 		/// </summary>
@@ -89,6 +95,9 @@ namespace MimeKit {
 		/// Gets the text of the text/plain alternative, if it exists.
 		/// </remarks>
 		/// <value>The text if a text/plain alternative exists; otherwise, <c>null</c>.</value>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public string TextBody {
 			get { return GetTextBody (TextFormat.Text); }
 		}
@@ -100,6 +109,9 @@ namespace MimeKit {
 		/// Gets the HTML-formatted text of the text/html alternative, if it exists.
 		/// </remarks>
 		/// <value>The HTML if a text/html alternative exists; otherwise, <c>null</c>.</value>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public string HtmlBody {
 			get { return GetTextBody (TextFormat.Html); }
 		}
@@ -119,11 +131,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitMultipartAlternative (this);
 		}
 
@@ -150,8 +167,13 @@ namespace MimeKit {
 		/// </remarks>
 		/// <returns>The text body in the desired format if it exists; otherwise, <c>null</c>.</returns>
 		/// <param name="format">The desired text format.</param>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public string GetTextBody (TextFormat format)
 		{
+			CheckDisposed ();
+
 			// walk the multipart/alternative children backwards from greatest level of faithfulness to the least faithful
 			for (int i = Count - 1; i >= 0; i--) {
 				var alternative = this[i] as MultipartAlternative;
diff --git a/MimeKit/MultipartRelated.cs b/MimeKit/MultipartRelated.cs
index eb260d5..2ba06ab 100644
--- a/MimeKit/MultipartRelated.cs
+++ b/MimeKit/MultipartRelated.cs
@@ -81,6 +81,12 @@ namespace MimeKit {
 		{
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("MultipartRelated");
+		}
+
 		int GetRootIndex ()
 		{
 			string start = ContentType.Parameters["start"];
@@ -113,6 +119,9 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="value"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public MimeEntity Root {
 			get {
 				int index = GetRootIndex ();
@@ -126,6 +135,8 @@ namespace MimeKit {
 				if (value == null)
 					throw new ArgumentNullException ("value");
 
+				CheckDisposed ();
+
 				int index;
 
 				if (Count > 0) {
@@ -169,11 +180,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitMultipartRelated (this);
 		}
 
@@ -188,6 +204,9 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="uri"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public bool Contains (Uri uri)
 		{
 			return IndexOf (uri) != -1;
@@ -210,11 +229,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="uri"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public int IndexOf (Uri uri)
 		{
 			if (uri == null)
 				throw new ArgumentNullException ("uri");
 
+			CheckDisposed ();
+
 			bool cid = uri.IsAbsoluteUri && uri.Scheme.ToLowerInvariant () == "cid";
 
 			for (int index = 0; index < Count; index++) {
@@ -263,6 +287,9 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="uri"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.IO.FileNotFoundException">
 		/// The MIME part for the specified URI could not be found.
 		/// </exception>
@@ -298,6 +325,9 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="uri"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		/// <exception cref="System.IO.FileNotFoundException">
 		/// The MIME part for the specified URI could not be found.
 		/// </exception>
diff --git a/MimeKit/TextPart.cs b/MimeKit/TextPart.cs
index 4924ff9..3621efd 100644
--- a/MimeKit/TextPart.cs
+++ b/MimeKit/TextPart.cs
@@ -158,6 +158,12 @@ namespace MimeKit {
 		{
 		}
 
+		void CheckDisposed ()
+		{
+			if (IsDisposed)
+				throw new ObjectDisposedException ("TextPart");
+		}
+
 		/// <summary>
 		/// Gets whether or not this text part contains enriched text.
 		/// </summary>
@@ -234,8 +240,13 @@ namespace MimeKit {
 		/// or <see cref="GetText(System.String)"/>.</para>
 		/// </remarks>
 		/// <value>The text.</value>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public string Text {
 			get {
+				CheckDisposed ();
+
 				if (ContentObject == null)
 					return string.Empty;
 
@@ -290,11 +301,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="visitor"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public override void Accept (MimeVisitor visitor)
 		{
 			if (visitor == null)
 				throw new ArgumentNullException ("visitor");
 
+			CheckDisposed ();
+
 			visitor.VisitTextPart (this);
 		}
 
@@ -332,11 +348,16 @@ namespace MimeKit {
 		/// <exception cref="System.ArgumentNullException">
 		/// <paramref name="encoding"/> is <c>null</c>.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public string GetText (Encoding encoding)
 		{
 			if (encoding == null)
 				throw new ArgumentNullException ("encoding");
 
+			CheckDisposed ();
+
 			if (ContentObject == null)
 				return string.Empty;
 
@@ -370,6 +391,9 @@ namespace MimeKit {
 		/// <exception cref="System.NotSupportedException">
 		/// The <paramref name="charset"/> is not supported.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public string GetText (string charset)
 		{
 			if (charset == null)
@@ -393,6 +417,9 @@ namespace MimeKit {
 		/// <para>-or-</para>
 		/// <para><paramref name="text"/> is <c>null</c>.</para>
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public void SetText (Encoding encoding, string text)
 		{
 			if (encoding == null)
@@ -401,6 +428,8 @@ namespace MimeKit {
 			if (text == null)
 				throw new ArgumentNullException ("text");
 
+			CheckDisposed ();
+
 			ContentType.Parameters["charset"] = CharsetUtils.GetMimeCharset (encoding);
 			var content = new MemoryStream (encoding.GetBytes (text));
 			ContentObject = new ContentObject (content);
@@ -424,6 +453,9 @@ namespace MimeKit {
 		/// <exception cref="System.NotSupportedException">
 		/// The <paramref name="charset"/> is not supported.
 		/// </exception>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The object has been disposed.
+		/// </exception>
 		public void SetText (string charset, string text)
 		{
 			if (charset == null)
diff --git a/MimeKit/Tnef/TnefPart.cs b/MimeKit/Tnef/TnefPart.cs
index bdff709..0c7c548 100644
--- a/MimeKit/Tnef/TnefPart.cs
+++ b/MimeKit/Tnef/TnefPart.cs
@@ -427,10 +427,10 @@ namespace MimeKit.Tnef {
 		/// </exception>
 		public IEnumerable<MimeEntity> ExtractAttachments ()
 		{
-			var message = ConvertToMessage ();
-
-			foreach (var attachment in message.BodyParts)
-				yield return attachment;
+			using (var message = ConvertToMessage ()) {
+				foreach (var attachment in message.BodyParts)
+					yield return attachment;
+			}
 
 			yield break;
 		}