使用 MailKit (C#) 转发电子邮件

Question

我正在尝试使用 MailKit（由jstedfast创建）访问 IMAP 帐户

我设法下载了消息（作为 MimeMessage），并且在某些时候我需要将它“转发”到另一个帐户。

如何最好地做到这一点，以保留原始电子邮件的所有信息（地址、标题、正文内容等）。

谢谢！

Answer 1

不同的人说“转发”时的意思不同，所以我想我会针对我能想到的不同含义提供答案。

1. 转发（重新发送）消息而不做任何更改。

“没有变化”，我的字面意思是原始消息数据根本没有变化。 这样做的方法是：

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：某些网络邮件提供商（例如 GMail、Hotmail/Office365 等）可能不允许您使用这种方法，因为他们可能认为这是电子邮件欺骗。 这些邮件主机可能会用您帐户的名称/电子邮件地址替换From标头，因此请注意这个潜在问题。

不过，通常人们并不是指这种类型的“转发”。 如果他们想重发，通常他们会使用下一种重发方法。

2. 以自动过滤器可能发送的方式转发（重新发送）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. 通过将邮件（整体）附加到新邮件来转发邮件，某些电子邮件客户端可能会这样做。

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. 以许多其他电子邮件客户端的方式“内联”转发邮件。

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);
}