there might have been answers to this many times. But I can't seem to find one that fits my issues so here we go:
I've ran an email server on my centos machine for over four months without problem, but had to remove and reinstall postfix/dovecot wiping their configurations. Now after setting everything up, I receive on average 43 Unknown mail returned to sender being dumped into my mailbox each hour. Each one containing scam/sex line messages with possible virus payloads in certain amounts of them. Before adding any configurations etc, could anyone give a rough sense of direction where the issue lies? I'm not running an open relay, or so I believe to be not running one. Tested via mxtoolbox.com etc. I've had Clamav on the machine since I ever got it, so I'm confidently ruling out any system compromise. But what troubles me is I get hundreds of these inside my /var/log/maillog file each minutes:
Does anyone have even a remote clue what could be causing this?