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Multiple A's per MX hostname vs. 1:1 A:MX all with equal priority vs. different priorities

From: Darren Pilgrim (postfixbitfreak.org)
Date: Thu Jan 15 2009 - 02:41:52 CST

A while back someone posted a message about how MTAs generally respond
to an unresponsive server given three different ways of setting up
multiple MX mail servers:

1. A single MX record with multiple A's for the hostname:

        example.com mail is handled by 10 a.mx.example.com
        a.mx.example.com has address 192.0.2.100
        a.mx.example.com has address 192.0.2.101
        a.mx.example.com has address 192.0.2.102

2. Multiple MX records with equal priority with a single A for each
hostname:

        example.com mail is handled by 10 a.mx.example.com
        example.com mail is handled by 10 b.mx.example.com
        example.com mail is handled by 10 c.mx.example.com
        a.mx.example.com has address 192.0.2.100
        b.mx.example.com has address 192.0.2.101
        c.mx.example.com has address 192.0.2.102
        
3. Multiple MX records with different priorities with a single A for
each hostname:

        example.com mail is handled by 10 a.mx.example.com
        example.com mail is handled by 20 b.mx.example.com
        example.com mail is handled by 30 c.mx.example.com
        a.mx.example.com has address 192.0.2.100
        b.mx.example.com has address 192.0.2.101
        c.mx.example.com has address 192.0.2.102

I can't find the message, mostly due to lack of sufficiently-narrow
search criteria. Would anyone who recalls the message post it?