How can I delete a message by message id with MailKit POP3 client?

Question

I want to use the MailKit Pop3Client to retrieve messages from a POP3 mailbox, and then delete these messages after processing. The retrieval code is something like:

Public Function GetMessages(Optional logPath As String = Nothing) As List(Of MimeMessage)

    Dim client As Pop3Client
    Dim messages = New List(Of MimeMessage)()

    Using client
        ConnectPop3(client)
        Dim count = client.GetMessageCount()
        For i As Integer = 0 To count - 1
            Dim msg = client.GetMessage(i)
            messages.Add(msg)
        Next
    End Using

    Return messages

End Function

My problem here is in order to delete a message in another message, I need an index, but that is long gone once I exit GetMessages. All I have is the info available on a MimeMessage object, but that has no index property, only MessageId, but in my Delete method, I would have to read all mails again, in order to look up an index value.

Now Pop3Client has a GetMessageUid(int index) method, which returns a mysterious string (looks like int) value with no apparent relation at all to the Mime MessageID, but it seems this is all I have. Then I have to store the MailKit Uid with each message, making my retrieval code something like this, using a dictionary to store uid-message pairs:

Public Function GetMessages(Optional delete As Boolean = False, Optional logPath As String = Nothing) As List(Of MimeMessage)

    Dim client As Pop3Client
    Dim messages = New Dictionary(Of String, MimeMessage)

    Using client
        ConnectPop3(client)
        Dim count = client.GetMessageCount()
        For i As Integer = 0 To count - 1
            Dim msg = client.GetMessage(i)
            Dim u = client.GetMessageUid(i)
            messages.Add(u, msg)
        Next
        client.Disconnect(True)
    End Using

    Return messages

End Function

I am really hoping I'm missing something here and what should be a really simple process is indeed simple, but I can't find anything else on my own.

score 3 · Accepted Answer · answered May 10 '15 at 00:58

3

The message UID is the only way to track a message between connections.

The index for a message can change as other messages are deleted.

Your options are:

Delete messages as you're downloading them.
Save the UID so you can come back and delete specific messages later.

It may make more sense if you skim through the POP3 RFC.

answered May 10 '15 at 00:58

Thanks. I had a, mistaken, impression that something like `GetMessageUid`, especially with a shiny client like MailKit, would return the `message-id` value for the message, but I'm heading back to the drawing board. – ProfK May 10 '15 at 05:06
But how do you delete a message by MessageID? `POP3.DeleteMessage()` only take index as argument. `folder.AddFlags` is only for imap, right? – MrCalvin May 30 '18 at 19:30
Maybe the only way is to iterate all messages and compare MessageID and the delete with the index, no shortcut, right? – MrCalvin May 30 '18 at 19:56

How can I delete a message by message id with MailKit POP3 client?

1 Answers1