使用 MailKit (C#) 轉發電子郵件

Question

我正在嘗試使用 MailKit（由jstedfast創建）訪問 IMAP 帳戶

我設法下載了消息（作為 MimeMessage），並且在某些時候我需要將它“轉發”到另一個帳戶。

如何最好地做到這一點，以保留原始電子郵件的所有信息（地址、標題、正文內容等）。

謝謝！

Answer 1

不同的人說“轉發”時的意思不同，所以我想我會針對我能想到的不同含義提供答案。

1. 轉發（重新發送）消息而不做任何更改。

“沒有變化”，我的字面意思是原始消息數據根本沒有變化。 這樣做的方法是：

var message = FetchMessageFromImapServer ();

using (var client = new SmtpClient ()) {
    client.Connect ("smtp.example.com", 465, true);
    client.Authenticate ("username", "password");

    var sender = new MailboxAddress ("My Name", "username@example.com");
    var recipients = new [] { new MailboxAddress ("John Smith", "john@smith.com") };

    // This version of the Send() method uses the supplied sender and
    // recipients rather than getting them from the message's headers.
    client.Send (message, sender, recipients);

    client.Disconnect (true);
}

注意：某些網絡郵件提供商（例如 GMail、Hotmail/Office365 等）可能不允許您使用這種方法，因為他們可能認為這是電子郵件欺騙。 這些郵件主機可能會用您帳戶的名稱/電子郵件地址替換From標頭，因此請注意這個潛在問題。

不過，通常人們並不是指這種類型的“轉發”。 如果他們想重發，通常他們會使用下一種重發方法。

2. 以自動過濾器可能發送的方式轉發（重新發送）消息。

var message = FetchMessageFromImapServer ();

// clear the Resent-* headers in case this message has already been Resent...
message.ResentSender = null;
message.ResentFrom.Clear ();
message.ResentReplyTo.Clear ();
message.ResentTo.Clear ();
message.ResentCc.Clear ();
message.ResentBcc.Clear ();

// now add our own Resent-* headers...
message.ResentFrom.Add (new MailboxAddress ("MyName", "username@example.com"));
message.ResentReplyTo.Add (new MailboxAddress ("MyName", "username@example.com"));
message.ResentTo.Add (new MailboxAddress ("John Smith", "john@smith.com"));
message.ResentMessageId = MimeUtils.GenerateMessageId ();
message.ResentDate = DateTimeOffset.Now;

using (var client = new SmtpClient ()) {
    client.Connect ("smtp.example.com", 465, true);
    client.Authenticate ("username", "password");

    // The Send() method will use the Resent-From/To/Cc/Bcc headers if
    // they are present.
    client.Send (message);

    client.Disconnect (true);
}

3. 通過將郵件（整體）附加到新郵件來轉發郵件，某些電子郵件客戶端可能會這樣做。

var messageToForward = FetchMessageFromImapServer ();

// construct a new message
var message = new MimeMessage ();
message.From.Add (new MailboxAddress ("MyName", "username@example.com"));
message.ReplyTo.Add (new MailboxAddress ("MyName", "username@example.com"));
message.To.Add (new MailboxAddress ("John Smith", "john@smith.com"));
message.Subject = "FWD: " + messageToForward.Subject;

// now to create our body...
var builder = new BodyBuilder ();
builder.TextBody = "Hey John,\r\n\r\nHere's that message I was telling you about...\r\n";
builder.Attachments.Add (new MessagePart { Message = messageToForward });

message.Body = builder.ToMessageBody ();

using (var client = new SmtpClient ()) {
    client.Connect ("smtp.example.com", 465, true);
    client.Authenticate ("username", "password");

    client.Send (message);

    client.Disconnect (true);
}

4. 以許多其他電子郵件客戶端的方式“內聯”轉發郵件。

var messageToForward = FetchMessageFromImapServer ();

// construct a new message
var message = new MimeMessage ();
message.From.Add (new MailboxAddress ("MyName", "username@example.com"));
message.ReplyTo.Add (new MailboxAddress ("MyName", "username@example.com"));
message.To.Add (new MailboxAddress ("John Smith", "john@smith.com"));
message.Subject = "FWD: " + messageToForward.Subject;

// now to create our body...
var builder = new BodyBuilder ();

using (var writer = new StringWriter ()) {
    var sender = messageToForward.From.Mailboxes.FirstOrDefault () ?? messageToForward.Sender;
    var senderName = sender != null ? (!string.IsNullOrEmpty (sender.Name) ? sender.Name : sender.Address) : "someone";
    var text = messageToForward.TextBody ?? string.Empty;

    writer.WriteLine ("On {0}, {1} wrote:", messageToForward.Date, senderName);

    using (var reader = new StringReader (text)) {
        string line;

        while ((line = reader.ReadLine ()) != null) {
            writer.Write ("> ");
            writer.WriteLine (line);
        }
    }

    builder.TextBody = writer.ToString ();
}

message.Body = builder.ToMessageBody ();

using (var client = new SmtpClient ()) {
    client.Connect ("smtp.example.com", 465, true);
    client.Authenticate ("username", "password");

    client.Send (message);

    client.Disconnect (true);
}