Peek message on IMAP server

If you are using GetMessageByUID to download email message or GetHeadersByUID to get only email headers, most IMAP servers will automatically mark such messages as seen. In other words IMAP server adds \SEEN flag to the messages you have downloaded.

If it’s not expected behavior in your scenario, you can use one of Peek* methods, such as: PeekHeadersByUID, PeekMessageByUID.

Using Peek methods

Those methods in contrast to their Get* equivalents (GetMessageByUID and GetHeadersByUID) do not set the \SEEN flag – emails are not marked as seen automatically.

The sample below connects to IMAP server finds all unseen messages, downloads them but does not change their unseen status. Messages are left unseen.

// C#

using(Imap imap = new Imap())
{
    imap.Connect("imap.server.com");
    imap.Login("user", "password");

    imap.SelectInbox();
    List<long> uidList = imap.SearchFlag(Flag.Unseen);
    foreach (long uid in uidList)
    {
        IMail email = new MailBuilder()
            .CreateFromEml(imap.PeekMessageByUID(uid));
        Console.WriteLine(email.Subject);
    }
    imap.Close();
}

' VB.NET

Using imap As New Imap
    imap.Connect("imap.server.com")
    imap.Login("user", "password")

    imap.SelectInbox()
    Dim uidList As List(Of Long) = imap.SearchFlag(Flag.Unseen)

    For Each uid As Long In uidList
        Dim email As IMail = New MailBuilder() _
            .CreateFromEml(imap.PeekMessageByUID(uid))
        Console.WriteLine(email.Subject)
    Next
    imap.Close()
End Using

There are Peek methods for downloading headers and even parts of the email message.

Examine instead of Select

The second approach is to use Examine method instead of Select. Examine puts the folder into read-only state, so no \SEEN flag is added to any message. The drawback is that you can not delete or upload any message.

// C#

using(Imap imap = new Imap())
{
    imap.Connect("imap.server.com");
    imap.Login("user", "password");

    imap.ExamineInbox(); // -or- imap.Examine("Inbox");

    // ...

    imap.Close();
}

' VB.NET

Using imap As New Imap
    imap.Connect("imap.server.com")
    imap.Login("user", "password")

    imap.SelectInbox()

    imap.ExamineInbox() ' -or- imap.Examine("Inbox")

    ' ...

    imap.Close()
End Using

You can also easily mark message as seen and unseen by using Imap.MarkMessageUnseenByUID and Imap.MarkMessageSeenByUID methods.

You can download Mail.dll IMAP client here.

Tags: C#, IMAP, Mail.dll, VB.NET

This entry was posted on Tuesday, July 6th, 2010 at 17:00 and is filed under Component. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.