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

2007-12-14 02:59:03

At 20:06 13/12/2007, Hector Santos wrote:

Arnt Gulbrandsen wrote:
So if I understand you correctly, you meant to say: «All current/modern DNS clients will support the resolution of a CNAME as part of a MX expansion process, when "current and modern" is defined to take this issue into account.»
That's just a tautology wrapped in some suggestive wording.

(Gawd, this is so silly.)


I guess that depends on how you view or define "Current and Modern."

I change my statement:

 "Industry ready DNS clients support the resolution of a
  CNAME as part of a MX expansion process."

Another else, IMO, is mal-practice. <g>

Can we move on?

Hector, the reason I'm 'debating' here is not because our software doesn't handle CNAME entries as MX records (it does), but because saying things like 'all modern' or 'all industry ready' or anything else which sounds like 'all good' is implying that anything that doesn't is poor quality or is breaking standards - when it most certainly isn't.

The debate comes up frequently of whether software should try to work around buggy implementations or fail them. Some people think you should do anything possible to make it work, others think you should fail anything which is slightly wrong, and most people are somewhere in between. One thing most agree on is that we should TRY to make sure everything works according to standards even if most software can work around the non-conformities. That means we should strongly discourage people putting CNAMES in as MX records - including telling them they're wrong if they do. It might work if you do, but that doesn't mean that it's an OK thing to do.

Saying that "anything which treats a buggy configuration as buggy is 'mal-practice'" is very dangerous IMHO. It could lead to people writing buggy implementations and saying 'xyz email client handles it so it must be right - ignore what the standards say, they're not what matters, what matters is common practice'.

IMHO, 2821bis should state that "putting CNAMES as the target of MX records is not allowed, as stated in RFC 2181"