BodyBuilderAttachments Property

public AttachmentCollection Attachments { get; }

            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 and I was hoping you could make it.

Will you be my +1?

-- Joey
";

            // In order to reference selfie.jpg from the html text, we'll need to add it
            // to builder.LinkedResources and then use its Content-Id value in the img src.
            var image = builder.LinkedResources.Add (@"C:\Users\Joey\Documents\Selfies\selfie.jpg");
            image.ContentId = MimeUtils.GenerateMessageId ();

            // Set the html version of the message text
            builder.HtmlBody = string.Format (@"<p>Hey Alice,<br>
<p>What are you up to this weekend? Monica is throwing one of her parties on
Saturday and I was hoping you could make it.<br>
<p>Will you be my +1?<br>
<p>-- Joey<br>
<center><img src=""cid:{0}""></center>", image.ContentId);

            // 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 ();