Re: Question about SMTP server environment

Is it necessary for the SMTP or web server to be set up as a domain
controller?

Not at all.

I always find my mail stuck in the queue. I suspect it is a DNS error causing a mail loop of some kind but am not sure what I need to do to fix it.

Do you have the same queue backlog regardless of whether you send to your local domain (which does indeed have to be set up properly in the SMTP service config) or to remote domains (which take no domain-specific configuration in the SMTP service, and whose DNS you obvs. do not control, and thus cannot change)?

Can someone direct me to a tutorial on MX...

MX records have nothing to do with outbound mail except in very special circumstances not worth contemplating here.

... and A records and how they interact
with SMTP servers and public and private DNS servers?

To ensure delivery to the widest range of remote systems, your outbound mail server needs to have a PTR for its public IP. That PTR needs to have a corresponding A record pointing back to the same IP. The SMTP HELO/EHLO greeting used by your server should be that same A record, the canonical hostname of your mail server.

HOWEVER, although all of the above are best practices, not following them cannot cause _all_ of your outbound mail to be backed up. The most likely explanations for the _complete_ backup are that (a) your mail server cannot resolve other domains' MX records using its configured DNS server (the configured resolver is broken), or (b) your mail server cannot connect to those MXs on TCP port 25 (blocked by firewall ACLs at your site or at your provider).

--Sandy
.

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