MimeKit 将附件添加到从 mht 文件加载的消息中

您好，我们正在尝试使用 MailKit 开发邮件发送系统。我们有一组使用 WORD 创建并保存为 MHTML 文件的电子邮件模板。当我们使用 MailKit 从 MHT 文件创建 MimeMessage 时，整个事情工作正常。

但是在创建此消息后，我无法找到添加附件的方法。

目前我们正在尝试以下措施。

private void SendEmail(string templatePath, List<string> attachments)
    {
        // Load the MHT Template
        var mimeMessage = MimeMessage.Load(templatePath);

        mimeMessage.From.Add(new MailBoxAddress("[email protected] /cdn-cgi/l/email-protection"));
        mimeMessage.To.Add(new MailBoxAddress("[email protected] /cdn-cgi/l/email-protection"));

        foreach (var attachment in attachments)
        {
            var fileAttachment = new MimePart()
            {
                ContentObject = new ContentObject(File.OpenRead(Path.Combine(attachment), ContentEncoding.Default),
                ContentDisposition = new ContentDisposition(ContentDisposition.Attachment),
                ContentTransferEncoding = ContentEncoding.Binary,
                FileName = Path.GetFileName(attachment)
            };

            // Attachments is a read only Enumerable here.
            mimeMessage.Attachments.Add
        }

    }

您需要遍历消息的 MIME 树结构，直到找到Multipart您想要添加“附件”，然后使用 Multipart.Add() 方法。

请记住，消息是嵌套的树结构，而不是只有 1 个消息正文（甚至只有 2 个）和附件列表的明确定义的结构。它比这复杂得多，所以 MimeMessage.Attachments 实际上没有办法“做正确的事情”。

对于一般情况，您可能可以这样做：

var message = MimeMessage.Load(fileName);
var attachment = new MimePart("application", "octet-stream") {
    FileName = attachmentName,
    ContentTransferEncoding = ContentEncoding.Base64,
    Content = new MimeContent(attachmentStream)
};

if (!(message.Body is Multipart multipart &&
      multipart.ContentType.Matches("multipart", "mixed"))) {
    // The top-level MIME part is not a multipart/mixed.
    //
    // Attachments are typically added to a multipart/mixed
    // container which tends to be the top-level MIME part
    // of the message (unless it is signed or encrypted).
    //
    // If the message is signed or encrypted, though, we do
    // do not want to mess with the structure, so the correct
    // thing to do there is to encapsulate the top-level part
    // in a multipart/mixed just like we are going to do anyway.
    multipart = new Multipart("mixed");

    // Replace the message body with the multipart/mixed and
    // add the old message body to it.
    multipart.Add(message.Body);
    message.Body = multipart;
}

// Add the attachment.
multipart.Add(attachment);

// Save the message back out to disk.
message.WriteTo(newFileName);