On Fri, Jul 15, 2016 at 9:33 PM, John Levine <jo...@taugh.com> wrote:
> >> I wasn’t sure if there is a specific > >> reason the preference is called out in the RFC. > > We wanted something consistent. > > >0 is the lowest preference MX and will therefore be tried first, > hopefully overriding any other higher preference MXs that may exist. > > The RFC specifically says that if you have a null MX, you can't > have any others. > But that's also part of the logic for specifying the precedence as "0" (zero). Even if there are others, they will never be considered. I wonder if some archaic (meaning not RFC 7505 aware) DNS provisioning systems only allow precedence that >= 1 (instead of allowing non-negative integer values). We have certainly encountered some that do not support a '.' value. Over-active and incorrect parsers are a bit of a bane. It's the old belt + braces approach :-) --Kurt
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