I've noticed that Portage's elog module for mailing is very simplistic when it comes to headers and envelope addresses. First, it sets neither From: nor To: and it is entirely hardcoded, when it comes to the Envelope-From ("portage"). What's worse, the hardcoded default is broken: it contains *no* domain name. While this way of doing things might work on local systems where you can relay everything you get via 127.0.0.1, using mod_mail.py on multiple systems which all mail via a central hub, things get messy. In its default configuration, for example, exim will refuse those messages (for the reasons outlined above). What's worse: The mail usually contains *no* hint besides the Received: headers from which machine it comes. I don't know if a better mod_mail.py is in the works, but if not, I can see whether I can put something together that works better - but it might need additional configuration vars in /etc/make.conf.
*** This bug has been marked as a duplicate of 116637 ***
