I am having a problem that is probably not a Webmin issue, but I’m not sure how to work around it. It manifests itself in many different ways, but essentially what is happening is that Webmin’s automated emails (in this particular example an email sent on Virtualmin scheduled backup failure to an external email account) is being rejected by my domainkeys filter (DK-Filter) before it even leaves my server via postfix because (I think) Webmin is sending as hostname.domain.com instead of domain.com as the sending address. Ironically, I receive the bounce message that the original message failed to send, but not the original webmin message.
Webmin sends its email as: trystan.acorp.net, but postfix/DK-filter kicks it out with the following messages:
Aug 23 05:00:52 trystan dk-filter[1582]: 4D6DA88E75: syntax error: missing or empty domain name in sender
Aug 23 05:00:52 trystan postfix/cleanup[8645]: 4D6DA88E75: milter-reject: END-OF-MESSAGE from localhost[127.0.0.1]: 5.7.1 Command rejected; from= to=
Aug 23 05:00:52 trystan spamd[16703]: prefork: child states: II
Aug 23 05:00:52 trystan postfix/cleanup[8645]: 4D6DA88E75: to=, orig_to=, relay=none, delay=7.4, delays=7.4/0/0/0,$
Aug 23 05:00:52 trystan postfix/cleanup[8677]: 5827088EBD: message id=<20090823100052.5827088EBD@trystan.acorp.net>
Aug 23 05:00:52 trystan postfix/qmgr[24814]: 5827088EBD: from=<>, size=2507, nrcpt=1 (queue active)
Aug 23 05:00:52 trystan postfix/bounce[8676]: 4D6DA88E75: sender non-delivery notification: 5827088EBD
Aug 23 05:00:52 trystan postfix/cleanup[8645]: 5FAB088DEC: message-id=<20090823100052.5827088EBD@trystan.acorp.net>
Aug 23 05:00:52 trystan postfix/qmgr[24814]: 5FAB088DEC: from=<>, size=2642, nrcpt=1 (queue active)
Aug 23 05:00:52 trystan postfix/local[8678]: 5827088EBD: to=, relay=local, delay=0.07, delays=0.02/0.01/0/0.05, dsn=2.0.0, status=se$
Aug 23 05:00:52 trystan postfix/qmgr[24814]: 5827088EBD: removed
Also, you may want to go into System Settings -> Module Config -> Defaults upon user and server creation, and set the “From: address for email sent by Virtualmin” field to the address you want it to use.