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

2007-12-13 00:58:19

On Dec 12, 2007, at 2:33 PM, Trevor Paquette wrote:

However, in talking to TrendMicro, they say that this syntax is perfectly valid and that RFC 2821 overrides the MX to CNAME limitation. The following website is their stance on this:

CNAMES returned for MX queries can cause problems.

In this case, the CNAME is a placeholder offered by a DNS provider who normally deals with websites. The name contained within the CNAME RR needs to be published as an MX record to avoid returning the CNAME itself.

Section 10.3 of RFC 2181 is fairly clear, where this section is not updated by the follow-on documents.

However, in talking to others, they say that TrendMicro is misinterpreting the RFC. I’ll admit after reading 2821, I could interpret things both ways.

RFC 2821 section 3.6 is somewhat misleading, and Ned has explained why fairly well.

This is why I come to you folks who are responsible for this RFC. Who is right? Is MX -> CNAME now allowed by 2821, or is TrendMicro in the wrong? 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. I don’t want to leave things left to misinterpretation.

The on-line advice published by Trend needs to be updated. AFAIK, the IMHS support staff will not make this recommendation.


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