Are you still using eZ publish 3.8.6? As far as I remember there were some bugs introduced in the mailing library which caused a part of the headers to be displayed in the body. I advice you to upgrade to the latest 3.8 release and check the result again. Good luck!
Do you have empty lines in your mail body?
If so, it's the famous "Bad Linefeeds in email" bug.
Search for "linefeed" and "mail" in the forums and bug database.
If this is the problem, you just need to change one ini setting in [MailSettings]. Please note, that this _should_ affect alle emails, AFAIK....
