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Re: MX to CNAME and (mis)interptretation of 2821

2008-02-12 23:06:43

<pseudo-chair hat on>

Consensus was reached on this issue:

1) MX => CNAME

In section 5.1, add to the end of the 1st paragraph:
    The result of an MX lookup MUST NOT be a CNAME.

</pseudo-chair hat off>

    Tony Hansen

Trevor Paquette wrote:
Sounds to me like this is a great opportunity to get this resolved once
and for all. If the intent of 2821 was never to override the provisions
of 2181, then Mr. Klensin could state this specifically within the RFC.

I believe that the confusion lies around the CNAME provision dealing the
left hand side of the MX record, not the right hand side. This is where
people get confused. The following paragraph can be interpreted to allow
CNAMES as the result of an MX lookup; this paragraph may need to be

5.1.  Locating the Target Host
 ..... The lookup first attempts to locate an MX record associated with
the name.  If a CNAME record is found instead, the resulting name is
processed as if it were the initial name.  If no MX records are found,
but an address RR (i.e., either an IPv4 A RR or an IPv6 AAAA RR, or
their successors) is found, the address RR is treated as if it was
associated with an implicit MX RR, with a preference of 0, pointing to
that host....
That is the section that is confusing people. You can read it to say
"When you do an MX record lookup, and the result is a CNAME, then ...
blah blah blah.." To the folks that I've talked to, they say that this
one statement allows an MX record to point to a CNAME. Again, if is this
not the case nor the intention, I'd love to see this latest revision
updated to categorically state that.

-----Original Message-----
From: owner-ietf-smtp(_at_)mail(_dot_)imc(_dot_)org 
On Behalf Of Frank Ellermann
Sent: Wednesday, December 12, 2007 4:13 PM
To: ietf-smtp(_at_)imc(_dot_)org
Subject: Re: MX to CNAME and (mis)interptretation of 2821

Trevor Paquette wrote:

Would it also be possible to state directly within the next
revision of the RFC where or not this RFC overrides the provision 10.3 of RFC 2181.

The Last Call for 2821bis ends 2007-12-24:

<> is 2821bis,
and <> is
a copy of the running Last Call.

I don't want to leave things left to misinterpretation.

I've seen at least one flamewar about this on another list.

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