Postfix: prevent relaying spam to local users


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[]
Mar 23 13:41:22 rex postfix/qmgr[17418]: 05A7A208176:, size=6003, nrcpt=1 (queue active)
Mar 23 13:41:22 rex postfix/local[853]: 05A7A208176:,, 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 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 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.