"The ViewSourceWith extension adds carriage returns in any text that has been edited even if the editor itself consistently uses newlines."
Vsw 0.8.1.1, Thunderbird 8.0, WinXP
I edit & save the file in my custom editor, then it correctly shows up in Tbird's "message editor",
but if the message is sent (or saved as a draft), Thunderbird adds CRs -- annoying!
It has nothing to do with the mail server.