I am trying to set up a perimeter spam and malware filter using CentOS/Postfix/SpamAssassin. Unfortunately, I am still stuck on the PostFix part. I've setup a new subdomain DNS with its own A/MX record (the MX points to the A), and that's working fine. I've also setup a basic PostFix conf using Webmin and editing the main.cf file according to http://www.postfix.org/STANDARD_CONFIGURATION_README.html, with an entry for
relay_domains = mailtest.mydomain.com. I send an email to
firstname.lastname@example.org expecting it to recognize
mailtest.mydomain.com as a relay domain, and at least get to the point of trying to figure out how to relay it (maybe there would be a failure in terms of looking up whether it is allowed to be relayed, where it's relayed to, the receiving host barfs, etc.) However, it never gets that far, and in my
maillog I see:
Apr 5 16:06:59 localhost postfix/smtpd: NOQUEUE: reject: RCPT from mailout- us.gmx.com[18.104.22.168]: 550 5.1.1 <jshin@mailtest.#####.com>: Recipient address rejected: User unknown in local recipient table; from=<email@example.com> to <jshin@mailtest.#####.com> proto=SMTP helo=<mailout-us.gmx.com>
...so I can conclude it's still trying to deliver locally.
Now, I have not disabled local delivery, mainly because I do not know how to do so. I would think however that it would at least try to relay it and match it against a domain.
One line in the main conf file that troubling to me was the following
# NOTE: Postfix will not automatically forward mail for domains that # list this system as their primary or backup MX host. See the # permit_mx_backup restriction description in postconf(5).
Where am I going wrong?