我可以使用 MailKit 通过电子邮件发送文件吗？

是的。这在文档和 常见问题中都有解释。

常见问题:

如何创建带附件的邮件？

要构造带附件的消息，首先需要创建一个 multipart/mixed容器，然后首先将消息体添加到该容器中。添加正文之后，可以向其中添加 MIME 部分，这些部分包含要附加的文件的内容，同时确保将 Content-Disposition头值设置为附件。您可能还希望在 Content-Disposition标头上设置 filename参数，以及在 Content-Type标头上设置 name参数。最方便的方法是使用 MimePart 文件名属性 将为您设置这两个参数，并将 Content-Disposition头值设置为 attachment(如果还没有设置为其他值)。

var message = new MimeMessage ();
message.From.Add (new MailboxAddress ("Joey", "joey@friends.com"));
message.To.Add (new MailboxAddress ("Alice", "alice@wonderland.com"));
message.Subject = "How you doin?";


// create our message text, just like before (except don't set it as the message.Body)
var body = new TextPart ("plain") {
Text = @"Hey Alice,


What are you up to this weekend? Monica is throwing one of her parties on
Saturday. I was hoping you could make it.


Will you be my +1?


-- Joey
"
};


// create an image attachment for the file located at path
var attachment = new MimePart ("image", "gif") {
Content = new MimeContent (File.OpenRead (path)),
ContentDisposition = new ContentDisposition (ContentDisposition.Attachment),
ContentTransferEncoding = ContentEncoding.Base64,
FileName = Path.GetFileName (path)
};


// now create the multipart/mixed container to hold the message text and the
// image attachment
var multipart = new Multipart ("mixed");
multipart.Add (body);
multipart.Add (attachment);


// now set the multipart/mixed as the message body
message.Body = multipart;

构造带有附件的消息的一种更简单的方法是利用 BodyBuilder 类。

var message = new MimeMessage ();
message.From.Add (new MailboxAddress ("Joey", "joey@friends.com"));
message.To.Add (new MailboxAddress ("Alice", "alice@wonderland.com"));
message.Subject = "How you doin?";


var builder = new BodyBuilder ();


// Set the plain-text version of the message text
builder.TextBody = @"Hey Alice,


What are you up to this weekend? Monica is throwing one of her parties on
Saturday. I was hoping you could make it.


Will you be my +1?


-- Joey
";


// We may also want to attach a calendar event for Monica's party...
builder.Attachments.Add (@"C:\Users\Joey\Documents\party.ics");


// Now we just need to set the message body and we're done
message.Body = builder.ToMessageBody ();

有关更多信息，请参见 创建消息。

@ jstedfast 带来了相当酷的解决方案，这里有一些简单的方法只是发送一个文件作为附件(pdf 文档在这种情况下，但可以应用到任何文件类型)的例子。

var message = new MimeMessage();
// add from, to, subject and other needed properties to your message


var builder = new BodyBuilder();
builder.HtmlBody = htmlContent;
builder.TextBody = textContent;


// you can either create MimeEntity object(s)
// this might get handy in case you want to pass multiple attachments from somewhere else
byte[] myFileAsByteArray = LoadMyFileAsByteArray();
var attachments = new List<MimeEntity>
{
// from file
MimeEntity.Load("myFile.pdf"),
// file from stream
MimeEntity.Load(new MemoryStream(myFileAsByteArray)),
// from stream with a content type defined
MimeEntity.Load(new ContentType("application", "pdf"), new MemoryStream(myFileAsByteArray))
}


// or add file directly - there are a few more overloads to this
builder.Attachments.Add("myFile.pdf");
builder.Attachments.Add("myFile.pdf", myFileAsByteArray);
builder.Attachments.Add("myFile.pdf", myFileAsByteArray , new ContentType("application", "pdf"));


// append previously created attachments
foreach (var attachment in attachments)
{
builder.Attachments.Add(attachment);
}


message.Body = builder.ToMessageBody();

希望能有帮助。

您还可以使用此方法直接发送多个文件。 * * 注意: 这里使用的文件是 IEnumable 文件 * *

        try
{
var message = new MimeMessage();
message.From.Add(new MailboxAddress(emailService.FromFullName, emailService.FromEmail));
message.To.AddRange(emailsToSend.Select(x => new MailboxAddress(x)));
message.Subject = subject;


var builder = new BodyBuilder();
builder.HtmlBody = body;


foreach (var attachment in files)
{
if (attachment.Length > 0)
{
string fileName = Path.GetFileName(attachment.FileName);
builder.Attachments.Add(fileName, attachment.OpenReadStream());
}
}
message.Body = builder.ToMessageBody();
           

}