From postfix-users  Mon Sep 16 12:54:57 2019
From: Wesley Peng <wesley () thepeng ! eu>
Date: Mon, 16 Sep 2019 12:54:57 +0000
To: postfix-users
Subject: Re: Refuse mail from hosts with closed port 25
Message-Id: <74274af4-b1c9-30bd-8a4a-798705e94ba7 () thepeng ! eu>
X-MARC-Message: https://marc.info/?l=postfix-users&m=156863855715611

Hi

on 2019/9/16 20:47, Paul van der Vlis wrote:
> How can I refuse mail from hosts who don't have an open port 25?
> 
> What do you think from such a check?

You shouldn't.

Many email systems have delivery agent and MTA to be separated.
That's to say, they get incoming mails from MTA which has port 25 
opened, but deliver outgoing messages via another gateway who doesn't 
have port 25 enabled.

regards.