How to move an attachment from one e-mail to another using MailKit/MimeKit?

Question

If we have the UniqueId to the mail we wish to move the attachment to via the usage of an ImapClient, how exactly can we achieve this?

Thank you!

Answer 1

UniqueId? AddAttachmentToMessage (ImapClient client, ImapFolder folder, UniqueId uid, MimeEntity attachment)
{
    var message = folder.GetMessage (uid);
    var body = message.Body;
    Multipart multipart;

    if (message.Body is Multipart && message.Body.ContentType.IsMimeType ("multipart", "mixed")) {
        multipart = (Multipart) message.Body;
    } else {
        multipart = new Multipart ("mixed");
        multipart.Add (message.Body);
        message.Body = multipart;
    }

    multipart.Add (attachment);

    var newUid = folder.Append (message);
    folder.AddFlags (uid, MessageFlags.Deleted, true);

    if (client.Capabilities.HasFlag (ImapCapabilities.UidPlus))
        folder.Expunge (new UniqueId[] { uid });

    return newUid;
}

If the server doesn't support UIDPLUS and you need the newUid value, then you can probably do something like this:

if (!client.Capabilities.HasFlag (ImapCapabilities.UidPlus)) {
    var initialUids = folder.Search (SearchQuery.All);
    folder.Append (message);
    var updatedUids = folder.Search (SearchQuery.All);

    // find the new uids
    var newUids = new UniqueIdSet (SortOrder.Ascending);
    for (int i = updatedUids.Count - 1; i >= 0; i--) {
        if (!initialUids.Contains (updatedUids[i]))
            newUids.Add (updatedUids[i]);
    }

    // get envelope info for each of the new messages
    var newItems = folder.Fetch (newUids, MessageSummaryItems.UniqueId | MessageSummaryItems.Envelope);
    foreach (var item in newItems) {
        var msgid = MimeUtils.ParseMessageId (item.Envelope.MessageId);

        if (message.MessageId.Equals (msgid))
            return item.UniuqeId;

        // Note: if you want to be more pedantic, you can compare the From/To/Cc/ReplyTo and Subject fields as well.
    }
}