From mboxrd@z Thu Jan  1 00:00:00 1970
From: robert@timetraveller.org (Robert Brockway)
Date: Thu, 21 Sep 2017 13:04:45 +1000 (AEST)
Subject: [TUHS] Who is running their own mail server and what do you run?
In-Reply-To: <b8e8c001-2e7e-c8dc-397f-a3c4ddb4ee56@tnetconsulting.net>
References: <20170920162502.GN25650@mcvoy.com>
 <201709201639.v8KGdGhC024387@darkstar.fourwinds.com>
 <83CD6BB4-9617-47F9-A87E-55C447D5F1CC@bitblocks.com>
 <alpine.DEB.2.11.1709210903320.3189@sirius.opentrend.net>
 <alpine.BSF.2.21.1709210957040.89458@aneurin.horsfall.org>
 <B2BBBAD6-6D45-4492-A4F9-2044BB113989@serissa.com>
 <b8e8c001-2e7e-c8dc-397f-a3c4ddb4ee56@tnetconsulting.net>
Message-ID: <alpine.DEB.2.11.1709211259480.3189@sirius.opentrend.net>

On Wed, 20 Sep 2017, Grant Taylor wrote:

> On 09/20/2017 07:30 PM, Lawrence Stewart wrote:
>> We have 3 MX records with weights 10 50 100, but only the second one has an 
>> SMTP server behind it.  This tends to discourage spammers.
>
> Do the first and third MX actually resolve to an IP?  Are they pingable?
>
> Are you sending TCP resets?

This is a well established technique known as Nolisting.  I believe the 
safest option is for the port to be unbound and thus for a TCP RST to be 
sent.

en.wikipedia.org/wiki/Nolisting

Rob