I had a question about Postfix’s smtpd DNS resolution.
In my logs (generally from spam sources), I see the following:
Feb 4 15:05:46 server postfix/smptd: warning: hostname 1-2-3-4.dyn.isp.net
does not resolve to address 18.104.22.168: Name or service not known
Does this mean that:
1. smtpd receives a connection from an smtp client and does a reverse DNS lookup
2. smtpd performs a forward DNS lookup on the result and compares the resulting
IP address to the initial IP
3. If the IP addresses don’t match it reports this error
... or is some other logic used to generate the error message ?