diff --git a/MimeKit/MailboxAddress.cs b/MimeKit/MailboxAddress.cs
index b75a42ece1..bc8dc62b38 100644
--- a/MimeKit/MailboxAddress.cs
+++ b/MimeKit/MailboxAddress.cs
@@ -312,6 +312,9 @@ static string EncodeAddrspec (string addrspec, int at)
 				var domain = addrspec.Substring (at + 1);
 				var local = addrspec.Substring (0, at);
 
+				if (ParseUtils.IsInternational (local))
+					local = ParseUtils.IdnEncode (local);
+
 				if (ParseUtils.IsInternational (domain))
 					domain = ParseUtils.IdnEncode (domain);
 
@@ -361,6 +364,9 @@ static string DecodeAddrspec (string addrspec, int at)
 				var domain = addrspec.Substring (at + 1);
 				var local = addrspec.Substring (0, at);
 
+				if (ParseUtils.IsIdnEncoded (local))
+					local = ParseUtils.IdnDecode (local);
+
 				if (ParseUtils.IsIdnEncoded (domain))
 					domain = ParseUtils.IdnDecode (domain);