I hope someone can help. With a bit of investigation, I'm sure I could source the answer to this but am in need of a quick fix hence posting this question.
I use an Exchange 2013 server purely for relaying mail from applications and services. Mails to one domain are failing with the error:
450 4.7.1 <server.domain.net>: Helo command rejected: Host not found
I have been told by the recipients that this is happening because the FQDN of our server does not resolve to a public IP address. So, my first question is, what type of record needs to be created for this? An A record I presume? We have public IP's available.
Secondly, when I have requested this record to be created I have been asked what inbound ports need to be allowed. Is there a simple list of these? I would presume: 25,443,80,465,993. Any others?
Thanks, and sorry for the slightly dumb questions.