Set envelope sender to the same as the From: address when PEAR mail is used. This is so that mail “bounces” to the expected place.
Note that this only works when $wgSMTP is set and (as a result) the PEAR mailer is used.
When $wgSMTP is not set, the envelope sender is set using $wgAdditionalMailParams set to something like “-f from@example.com”. Someone should create some Envelope sender sanity in how the envelope sender is set.
Suggestion: if $wgAdditionalMailParams is not set, then use $wgEmergencyContact to create “-f $wgEmergencyContact” for php mailer and to set the Return-Path header for PEAR mailer. I used “From:” for Return-Path here because it seemed most sensible.
See also:
http://pear.php.net/bugs/bug.php?id=5017