FAQ.md

Frequently Asked Questions

Question Index

• How can I get a protocol log for IMAP, POP3, or SMTP to see what is going wrong?
• Why doesn't MailKit find some of my GMail POP3 or IMAP messages?
• How can I log in to a GMail account using OAuth 2.0?
• How can I search for messages delivered between two dates?
• What does "The ImapClient is currently busy processing a command." mean?
• Why do I get InvalidOperationException: "The folder is not currently open."?
• ImapFolder.MoveTo() does not move the message out of the source folder. Why not?
• How can I mark messages as read using IMAP?

How can I get a protocol log for IMAP, POP3, or SMTP to see what is going wrong?

All of MailKit's client implementations have a constructor that takes a nifty IProtocolLogger interface for logging client/server communications. Out of the box, you can use the handy ProtocolLogger class. Here are some examples of how to use it:

// log to a file called 'imap.log'
var client = new ImapClient (new ProtocolLogger ("imap.log"));

// log to standard output (i.e. the console)
var client = new ImapClient (new ProtocolLogger (Console.OpenStandardOutput ()));

Why doesn't MailKit find some of my GMail POP3 or IMAP messages?

By default, GMail's POP3 and IMAP server does not behave like standard POP3 or IMAP servers and hides messages from clients using those protocols (as well as having other non-standard behavior).

If you want to configure your GMail POP3 or IMAP settings to behave the way POP3 and IMAP are intended to behave according to their protocol specifications, you'll need to log in to your GMail account via your web browser and navigate to the Forwarding and POP/IMAP tab of your GMail Settings page and set your options to look like this:

How can I log in to a GMail account using OAuth 2.0?

The first thing you need to do is follow Google's instructions for obtaining OAuth 2.0 credentials for your application.

Once you've done that, the easiest way to obtain an access token is to use Google's Google.Apis.Auth library:

var certificate = new X509Certificate2 (@"C:\path\to\certificate.p12", "password", X509KeyStorageFlags.Exportable);
var credential = new ServiceAccountCredential (new ServiceAccountCredential
    .Initializer ("your-developer-id@developer.gserviceaccount.com") {
    // Note: other scopes can be found here: https://developers.google.com/gmail/api/auth/scopes
    Scopes = new[] { "https://mail.google.com/" },
    User = "username@gmail.com"
}.FromCertificate (certificate));

bool result = await credential.RequestAccessTokenAsync (cancel.Token);

// Note: result will be true if the access token was received successfully

Now that you have an access token (credential.Token.AccessToken), you can use it with MailKit as if it were the password:

using (var client = new ImapClient ()) {
    client.Connect ("imap.gmail.com", 993, true);
    
    // use the access token as the password string
    client.Authenticate ("username@gmail.com", credential.Token.AccessToken);
}

How can I search for messages delivered between two dates?

The obvious solution is:

var query = SearchQuery.DeliveredAfter (dateRange.BeginDate)
    .And (SearchQuery.DeliveredBefore (dateRange.EndDate));
var results = folder.Search (query);

However, it has been reported to me that this doesn't work reliably depending on the IMAP server implementation.

If you find that this query doesn't get the expected results for your IMAP server, here's another solution that should always work:

var query = SearchQuery.Not (SearchQuery.DeliveredBefore (dateRange.BeginDate)
    .Or (SearchQuery.DeliveredAfter (dateRange.EndDate)));
var results = folder.Search (query);

What does "The ImapClient is currently busy processing a command." mean?

If you get an InvalidOperationException with the message, "The ImapClient is currently busy processing a command.", it means that you are trying to use the ImapClient and/or one of its ImapFolders from multiple threads. To avoid this situation, you'll need to lock the SyncRoot property of the ImapClient and ImapFolder objects when performing operations on them.

For example:

lock (client.SyncRoot) {
    client.NoOp ();
}

Note: Locking the SyncRoot is only necessary when using the synchronous API's. All Async() method variants already do this locking for you.

Why do I get InvalidOperationException: "The folder is not currently open."?

If you get this exception, it's probably because you thought you had to open the destination folder that you passed as an argument to one of the CopyTo() or MoveTo() methods. When you opened that destination folder, you also inadvertantly closed the source folder which is why you are getting this exception.

The IMAP server can only have a single folder open at a time. Whenever you open a folder, you automatically close the previously opened folder.

When copying or moving messages from one folder to another, you only need to have the source folder open.

ImapFolder.MoveTo() does not move the message out of the source folder. Why not?

If you look at the source code for the ImapFolder.MoveTo() method, what you'll notice is that there are several code paths depending on the features that the IMAP server supports.

If the IMAP server supports the MOVE extension, then MailKit's MoveTo() method will use the MOVE command. I suspect that your server does not support the MOVE command or you probably wouldn't be seeing what you are seeing.

When the IMAP server does not support the MOVE command, MailKit has to use the COPY command to copy the message(s) to the destination folder. Once the COPY command has completed, it will then mark the messages that you asked it to move for deletion by setting the \Deleted flag on those messages.

If the server supports the UIDPLUS extension, then MailKit will attempt to EXPUNGE the subset of messages that it just marked for deletion, however, if the UIDPLUS extension is not supported by the IMAP server, then it cannot safely expunge just that subset of messages and so it simply stops there.

My guess is that your server supports neither MOVE nor UIDPLUS and that is why clients like Outlook continue to see the messages in your folder. I believe, however, that Outlook has a setting to show deleted messages with a strikeout (which you probably have disabled).

So to answer your question more succinctly: After calling folder.MoveTo (...);, if you are confident that the messages marked for deletion should be expunged, call folder.Expunge ();

How can I mark messages as read for IMAP?

The way to mark messages as read using the IMAP protocol is to set the \Seen flag on the message(s).

To do this using MailKit, you will first need to know either the index(es) or the UID(s) of the messages that you would like to set the \Seen flag on. Once you have that information, you will want to call one of the AddFlags() methods on the ImapFolder. For example:

folder.AddFlags (uids, MessageFlags.Seen, true);

To mark messages as unread, you would remove the \Seen flag, like so:

folder.RemoveFlags (uids, MessageFlags.Seen, true);