PTR record/rDNS for mail server considered "generic" or a "dynamic IP"

Sefam asked:

I’m currently trying to figure out how to configure my rDNS to be SpamAssassin friendly.

SpamAssassin’s documentation only seems to provide the following;

https://wiki.apache.org/spamassassin/Rules/CK_HELO_DYNAMIC_SPLIT_IP

“The HELO appeared to be suspicious. This is typically the result of a poorly configured email server advertising itself as XXX-XXX-XXX-XXX.hostname.tld (where XXX is an IP address).”

Currently, my rDNS is set as follows on the ISP’s side;

XX.XXX.XXX.XX.static.domainname.com

domainname obviously being my domain name. Originally, it was that but without the “static” part, I tried doing this as the documentation on what is an acceptable “static” and “non-generic” rDNS would be. Didn’t seem to fix the issue. I’ve also tried using the following service; https://www.debouncer.com/reverse-dns-check

I’m currently Postfix/Dovecot on FreeBSD, and using cloudflare for my DNS (Exclusively in DNS only mode as cloudflare itself doesn’t support email traffic), I’ve set up an A record to point my reverse DNS towards my server’s IP so that it resolves.

What should I do to mitigate this issue? My guess currently would be to remove the IP entirely from the rDNS record.

My answer:


This complaint is specifically about the IP address appearing in some form in the PTR record. This is not advisable for a variety of reasons, one of which as you’ve discovered is that many destinations will mark your mail as spam or reject it outright.

Set the PTR record to something appropriate, which does not include the IP address. The actual FQDN of the server is usually the best bet.


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