MailMate allows message with bad header to be sent

It is possible to create bad headers by pasting image files into the subject line:

Mehrfachauswahl und Abbrechen-ButtonsIMG_0358.PNG\x{0d}IMG_0357.PNG

I noticed I pasted them, but they disappeared when I clicked somewhere else (because they probably got moved into a second line or something similar), so I did not worry about them anymore. That will result in the following error message when viewing that message in the Sent folder:

WARNING: bad headers - Improper use of control character (char 0D hex):
 Subject: ...und Abbrechen-ButtonsIMG_0358.PNGIMG_0357.PNG

I think MailMate should have checks against sending out bad headers.