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Re: [ietf-smtp] EHLO domain validation requirement in RFC 5321

2020-09-28 03:39:14

On 28 Sep 2020, at 03:00, Keith Moore <moore(_at_)network-heretics(_dot_)com> 

On 9/27/20 9:51 PM, Sam Varshavchik wrote:

Keith Moore writes:

I thought it was about advice to the server which is currently that the 
server MUST NOT refuse to accept a message based on failure of EHLO 
argument verification.

My argument is that EHLO verification is, in the long run, poor practice 
and should not be encouraged by 5321bis even if it seems like an effective 

To me, "SHOULD NOT" is a better match for "should not be encouraged". The 
current phrasing, "MUST NOT", prohibits it.

I might agree with that, though I would also like to see some elaboration as 
to why it's a Bad Idea in the long run, rather than just SHOULD NOT.

(I have a little but of trouble with the current 5321 language, because it 
conflicts with the notion that an SMTP server can reject mail for any reason. 
   At best the juxtaposition of these two seems conflicting and confusing 
even though I think that EHLO verification is overall a shortsighted idea 
that should be discouraged.)

Whether or not EHLO domain validation is prohibited or not, it is used in 
practice right now, and the current language in 5321 is being ignored, to 
some degree. The same language also existed in 2821, so this has been 
ignored for a while. An Internet standard that does not reflect current 
practice is not as valuable as one which is.

I actually disagree.   The purpose of a protocol specification standard 
should not be to reflect current practice; it should be to specify desirable 
practice.    And it's important to not confuse the two goals.

However I will admit that if the standard specifies a practice that doesn't 
interoperate well with current practice, it can harm the effectiveness of the 

Do you think if the wording in the RFC is changed that established behavior 
will change? That the SMTP servers will be reconfigured to stop doing what they 
are doing? 


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