Question Configure e-mail incoming / outgoing server

[vincentx3]

Server operating system version

20.04

Plesk version and microupdate number

Plesk Obsidian Web Admin 18.0.52

Hello everyone,
Admittedly, a somewhat "stupid" question, but currently I don't seem to understand something or am doing something fundamentally wrong.

My mail server is currently configured as follows, i.e. SPF, DMARC and DKIM

Plesk runs with a firewall, just for fun I "played" with the incoming and outgoing mail servers when configuring the e-mails via Thunderbird
Egro: no matter what I take, it works as long as there is a .XYZ.com.

My question:
How can I configure it so that only a specific server (e.g. mail.XYZ.com or XYZ.com) is allowed and the rest result in an error.

I'm currently approaching Plesk / Linux / DNS

About the system:
Linux 20.04
Plesk Obsidian
postfix as mail server
Firewall enabled


Thank you very much

 

[Peter Debik]

The server can always be addressed by all domains that point to the same ip address. SSL/TLS encryption does not work in such cases, but nevertheless a connection is possible. I could imagine that you can create an iptables (firewall) rule that blocks traffic based on a logical AND for domain names NOT matching a certain pattern AND at the same time limited to only certain ports (the mail ports 993, 995, 143, 465, 587, but not 25), but such a construct would be quite odd. That however will still leave port 25 open, which is a necessity, and also allow clients to connect using an IP address instead of the hostname.

All in all, just don't do it. It will only create problems and not improve anything.