如何使用 MailKit/MimeKit 将附件从一封电子邮件移动到另一封电子邮件？

Question

如果我们有UniqueId 到我们希望通过使用ImapClient 将附件移动到的邮件中，我们究竟如何才能做到这一点？

谢谢！

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;
}

如果服务器不支持 UIDPLUS 并且您需要 newUid 值，那么您可以这样做：

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.
    }
}