[Mimedefang] Potential for Business mail servers tonot havereverse DNS

John Rudd john at rudd.cc
Sat Sep 23 01:30:16 EDT 2006

Les Mikesell wrote:
> On Fri, 2006-09-22 at 20:32, John Rudd wrote:
>> Kevin A. McGrail wrote:
>>>> By "strict interpretation", I mean "enforce all of these as MUST 
>>>> directives, instead of mere SHOULD directives/suggestions".
>>> I disagree with this statement but would like to have you review the 
>>> code I'm about to post.  RFC's use MUST/SHOULD on purpose and you must 
>>> not reinterpet the should's as must's just because you like it better ;-)
>> Actually, given what SHOULD means (that those who fail to obey them 
>> should fully consider the consequences of that action), and the text of 
>> the RFC that I quoted (which warns that failure to comply could result 
>> in service rejections), it's perfectly reasonable for a site to make 
>> those recommendations into requirements for service (which is all I was 
>> indicating).
> If a SHOULD could be interpreted as a requirement, there
> wouldn't be any MUST's.

There is absolutely no logic to your statement.

A MUST is _always_ a requirement.  Even if a SHOULD is sometimes treated 
as a requirement for service (as that RFC clearly states) it does not 
displace the need for MUSTS, because a SHOULD is _not_ _always_ a 
requirement for service.

And, there is nothing in the definition of the RFC use of the term 
"SHOULD" which says you MUST NOT treat a SHOULD as a requirement for 
service.  The most you can say is that making a SHOULD a requirement for 
service is as cautionary to those who choose deny service on a SHOULD as 
it is cautionary to those who would choose to not adhere to the SHOULD.

In this specific case, the SHOULD outlines the consequence of not 
adhering to the SHOULD.  The purpose of a SHOULD is to allow deviation 
but to caution those who would do so.  By making it a requirement for 
service, the implementers of that policy are applying those 
consequences.  They are not abusing the purpose of a SHOULD, confusing 
it with a MUST, nor obsoleting the concept of a MUST.  To suggest so is 

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