spam from non-account on internal domain
On my zimbra server I have several domains. Lately I've been seeing spam coming from a non-existent account on one of my internal domains. All the messages are coming from email@example.com where * = a random number.
I'd like to block this spam without affecting legitimate users that do have accounts on mydomain.com. Is this possible? I was thinking something like block all mail from firstname.lastname@example.org if random-user does not have an actual account.
I am also open to other suggestions. The above was just the first idea that popped into my head.
Let me know if any more details are required.
Release 7.2.0_GA_2669.RHEL6_64_20120410002025 CentOS6_64 FOSS edition.