Weird PRT requirement

[exander77]

Reverse name(s) name.example.com for ip xxx.xxx.xxx.xxx do not match hostname mail.example.com, which will cause other mail servers to reject incoming messages from this IP.

I am getting a variant of this message.
This is not the requirement that exists.

IP address has to have PTR and PTR record has to forward resolve to IP address. But mail server hostname can be entirely different.

For example:

# host alpha.domain.com
alpha.domain.com has address 11.10.9.8
# host 11.10.9.8
8.9.10.11.in-addr.arpa domain name pointer alpha.domain.com.

With mail.domain.com mail server address is entirely valid configuration as far as I am aware.

[mjl-]

I think you're right that the IP hostname doesn't have to be the hostname configured for mox (the machine).
From memory, mox be doing this just to keep the configuration/setup straightforward.
Is there a use-case/reason to have a different hostname in mox (which uses the hostname during smtp ehlo) than in reverse dns?

[exander77]

I think you're right that the IP hostname doesn't have to be the hostname configured for mox (the machine). From memory, mox be doing this just to keep the configuration/setup straightforward. Is there a use-case/reason to have a different hostname in mox (which uses the hostname during smtp ehlo) than in reverse dns?

A single IP address can generally serve multiple services, especially with virtualization and containers. RDNS usually leads to the hostname of the host system, sure you can have multiple RDNS, but almost nobody does that. The virtual machines or containers that handle services provided by the system are usually named differently. It may even be an entirely different system. Many servers may be hosted behind a single external IP.