Multipart emails not handled correctly

One of my plugins sends a multipart/alternative message when posts are changed. Unfortunately, the way these messages are parsed by Mail Bank, they arrive incorrectly formatted. The text version has no newlines at all, and both versions include message headers (Content-Type: text/whatever) in the message text, as well as the message part boundary following the body.

Is there a chance this parsing could be adjusted to properly split out the text and HTML bodies?