Explicit priority MX with only AAAA record

Marcus Stoegbauer ms at man-da.de
Wed Jun 25 15:32:50 CEST 2008


Steve Bertrand wrote:
> I can't really come up with a conclusive answer to hopefully a simple 
> question.
> Currently, I have an MX for smtp.ibctech.ca. This name holds both an A, 
> and an AAAA record.
> I've been considering breaking that, and having separate explicit MX 
> records for each an A and an AAAA record, and setting the IPv6 MX as 
> priority, the v4 as next priority.

We had this setup for about 1.5 years for our (really small) company 
domain and I didn't receive any complaints during this time that mails 
couldn't be delivered or got lost.
However there are said to be mail daemons which don't behave well when 
the first MX can't be resolved to an A record and stop delivering the 
mail altogether.

> Before I go test this on the one MX box I have and possibly cause myself 
> grief, does anyone know if there will be negative effects for v4 only 
> clients?

I don't see the upside on changing from "AAAA/A" to "first AAAA, then 
A". In my eyes your current setup is the best and easiest solution 
because it should give you exactly the same behaviour, no matter which 
IP protocol you're using.


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