changing emails to be sent from somebody other than nobody

Hi,

I think this has been discussed here before, but after doing a search on "nobody" I could find no results.

My website has forums which send out messages via email to various users at various time. Problem is they get sent from nobody@zzzz.xxxx.yyyy.com and some email filters identify them as spam. It didn't seem to matter whether I had the checkbox "allow emails from nobody" in the tweak settings checked or not, the emails still came from nobody@.

Is there any way to fix this?