[GRLUG] Postfix HELO issue

[Grand Rapids Linux Users Group]

On Thu, 5 Aug 2021, Grand Rapids Linux Users Group wrote:

> Yes, many, but not all, SMTP servers require a fully valid hostname, with
> domain, in the HELO.
>
The subdomain is valid (MX, DKIM, DMARC all validate), .. and reverse DNS
matches the full hostname:

$ host majordomo.mailman.dd.org
majordomo.mailman.dd.org has address 24.38.nn.134

; <<>> DiG 9.16.6 <<>> -x 24.38.dd.134

;; QUESTION SECTION:
;134.dd.38.24.in-addr.arpa.	IN	PTR

;; ANSWER SECTION:
134.dd.38.24.in-addr.arpa. 86400 IN	PTR
majordomo.mailman.dd.org.

> Often then will do a lookup on it in DNS to make sure it is real/exists as
> well. Some even insist that the IP they get match the IP that the SMTP
> connection is from.
>
Any thought on how to determine if is actually a subdomain problem?

	Thanks!!