On 6/25/2024 10:51 AM, Jim Dory wrote:
2. SMTP: Reverse DNS doesn't match SMTP Banner (The SMTP banner issued
by your email server did not contain the hostname we resolved for your
server’s IP address.)
That itself is suspicious (to a receiving MTA). And as Dmitri pointed
out, multiple PTR records is also a problem.
Remember that many email systems look for "circular resolution" where
eventually an A's address matches a PTR's name.
Example:
lists.x.com -> smtp.x.com (CNAME)
smtp.x.com -> 1.2.3.4 (A)
1.2.3.4 -> mail.p.com (PTR)
mail.p.com -> 1.2.3.4 (A)
("equilibrium has been reached")
If 1.2.3.4 resolves to both mail.x.com and maybe mailhost.x.com (which
might not have a matching A record), sometimes the magic smoke will come
out :).
z!
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