[ietf-dkim] lets add one more shall we?

[Charles Lindsey]

On Thu, 07 Jun 2007 14:41:22 +0100, Hector Santos <hsantos at santronics.com>  
wrote:

> Charles Lindsey wrote:
>
>>> In other words, not all MX query gives you IP addresses to try.
>>  So in that case, you can have an MX that directs you to the domain  
>> nomail.invalid (which has no A record, of course) and that is the end  
>> of the matter. What is wrong with that?
>
> A change in long establish SMTP semantics and sending strategies.

No. Just a way to say this domain does not want to receive any email, even  
though it has an A record. That MX should get cached (so no excessive load  
on the authoritative server). And nomail.invalid should also get cached,  
as a DNS failure, or so I have been informed, so no excessive load on the  
root servers; a smart DNS resolver will already have built into it that  
'invalid' is not even worth looking up. I proposed it as an alternative to  
the suggested "MX .", which apparently had problems.

> Each implementation may have  their own set of wrappers, for example in  
> Wildcat! SMTP,  if enabled by the sysop, failure to deliver after the X  
> number of retries may get the domain blacklisted.  We also have a CBV  
> (SMTP callback) and NXDOMAIN failures promotes 45x responses.  It works  
> like a GREYLIST hence bad systems don't try again, good systems do.

A domain which does not want to receive email should welcome such  
blacklisting. Agreed it should be reviewed after some TTL.

-- 
Charles H. Lindsey ---------At Home, doing my own thing------------------------
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   Web: http://www.cs.man.ac.uk/~chl
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