net-mail/mailman-2.1.8_rc1 uses the gid "qmail" when building with USE="qmail", but qmail (as documented in qmail-lspawn) uses the uid/gid of the mailman user when delivering mail to the mailman user (when delivering a mail to a mailing list for example). This results in the following error in the qmail log: @4000000044969fd023eb03d4 delivery 113: deferral: Group_mismatch_error.__Mailman_expected_the_mail/wrapper_script_to_be_executed_as_group_"qmail",_but/the_system's_mail_server_executed_the_mail_script_as/group_"mailman".__Try_tweaking_the_mail_server_to_run_the/script_as_group_"qmail",_or_re-run_configure,_/providing_the_command_line_option_`--with-mail-gid=mailman'./ Replacing the gid qmail with mailman in the ebuild makes everything work as expected.
Can't test it (no qmail around), so I need to trust you, but fixed it. Please re-open if any problems occur due to this.
done
Works for me now (although when testing for the first time I put "mailman" instead of "280" as uid)...