[prev in list] [next in list] [prev in thread] [next in thread] 

List:       postfix-users
Subject:    Re: Refuse mail from hosts with closed port 25
From:       "Bill Cole" <postfixlists-070913 () billmail ! scconsult ! com>
Date:       2019-09-16 14:16:37
Message-ID: A14E2EC1-F13A-40F8-B193-14C219787706 () billmail ! scconsult ! com
[Download RAW message or body]

On 16 Sep 2019, at 9:17, Paul van der Vlis wrote:

> I guess only the big
> providers will have different servers for inbound and outbound email,
> and you can make a list of them.

Bad guess.

Many business email systems are architected this way for security 
purposes (e.g. Exchange is fine for sending mail out but you really 
don't want it accepting email from the Internet directly...) This is 
especially common with older businesses who got generous IPv4 
allocations decades ago, however I have worked with mail systems serving 
less than 500 employee-users of companies with /29 allocations that have 
mail going out from a shared NAT address but coming in via a dedicated 
IP.

-- 
Bill Cole
bill@scconsult.com or billcole@apache.org
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
[prev in list] [next in list] [prev in thread] [next in thread]