[dns-operations] MX record definition?

Edward Lewis Ed.Lewis at neustar.biz
Wed Dec 17 23:54:45 UTC 2008

That's the place for the definition.

Don't know if there's a document that says why/that they are bad.

I can only venture a guess - probably because the reason they are bad 
is weakly written application code that assumes the name in the MX 
record is a host name and not a domain name.  (Host names in RFC 
1123.)  I.e., what do you get if you try to look up the A record for 

As far as being a no-no: they aren't prohibited by the DNS 
specification.  Perhaps there's a mail protocol restriction.

At 15:21 -0800 12/17/08, Seth Mattinen wrote:
>Does anyone know offhand where the MX record is defined? The best I 
>can find is section 3.3.9 in RFC 1035. I'm trying to find a 
>reference that says numeric MX records are bad. I'm assuming they're 
>a no-no, at least that's what I've always been told.
>dns-operations mailing list
>dns-operations at lists.dns-oarc.net

Edward Lewis
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