Hi,
One of my users has reported a lot of spam which is being sent through my server using the same domain name. I checked the mail log:
Mar 23 13:41:20 rex postfix/smtpd[8276]: 05A7A208176: client=unknown[175.xxx.xxx.xxx]
Mar 23 13:41:22 rex postfix/qmgr[17418]: 05A7A208176: from=<USERNAME@MYDOMAIN.co.uk>, size=6003, nrcpt=1 (queue active)
Mar 23 13:41:22 rex postfix/local[853]: 05A7A208176: to=<USERNAME@HOSTNAME.co.uk>, orig_to=<USERNAME@MYDOMAIN.co.uk>, relay=local, delay=2.1, delays=2/0/0/0.05, dsn=2.0.0, status=sent (forwarded as 0A0812081C8)
I'm pretty sure Postfix is configured to not allow relaying to external domains and a scan on mxtoolbox.com says "OK - Not an open relay".
So, can I prevent this happening and would any changes have any knock-on effects?
I didn't want to post the whole main.cf unnecessarily but this bit might be relevant:
smtpd_recipient_restrictions = reject_non_fqdn_recipient reject_unknown_recipient_domain permit_mynetworks permit_sasl_authenticated reject_unauth_destination reject_non_fqdn_hostname reject_invalid_hostname permit
I'd be grateful for any help.
Thanks,
Martin.