Thanks! Filling the templates with text worked. Maybe you could fill those with some default text when Front End PM (PRO) is installed so it would work from the beginning.
I have a problem with the message_url variable:
The ampersand in the url is urlencoded into & by you and this breaks the url so it does not correctly handle the fep_id anymore.
The message url as is is sent: https://my.domain.com/?fepaction=viewmessage&fep_id=12660
The message url should be: https://my.domain.com/?fepaction=viewmessage&fep_id=12660