Just installed a Gentoo server with exim and mailman. Messages sent from mailman would not be delivered. This is because the ::1 address is not included in the relay_from_hosts variable.
So this bug is just about setting a sensible default for the relay_from_hosts variable in the /etc/exim/exim.conf.dist file, it should look like this:
hostlist relay_from_hosts = 127.0.0.1 : ::::1
Steps to Reproduce:
1. Setup exim & mailman
2. Test by creating a mailing list, it sends an email to the mailing list owner
See the exims logs, messages are rejected with the message:
H=localhost (...) [::1] F=<...> rejected RCPT <...>: relay not permitted