Re: [ietf-smtp] EHLO domain validation requirement in RFC 5321
Sam Varshavchik <mrsam@courier-mta.com> Sun, 27 September 2020 12:58 UTC
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From: Sam Varshavchik <mrsam@courier-mta.com>
To: ietf-smtp@ietf.org
Date: Sun, 27 Sep 2020 08:58:31 -0400
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Subject: Re: [ietf-smtp] EHLO domain validation requirement in RFC 5321
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Keith Moore writes: > 3. 821, 1123, and subsequent revisions all seem to be based on the > assumption that if you're operating an SMTP server, you're trying in good > faith to deliver (legitimate) email reliably. I'm not sure this assumption And you should have a pretty good idea of what your IP address is. > Seen from that perspective, maybe 5321's language about EHLO arguments could > use some updating along the following lines: > > - For a very many reasons [which could be listed, or not], SMTP servers have > no reasonable expectation of being able to determine the validity or > legitimacy of a message based on comparison of the EHLO command argument > with anything else at all. Therefore if what you're trying to do is > reliably deliver legitimate mail (for some meaning of legitimate), > validation of EHLO arguments is useless and strongly NOT RECOMMENDED. The exact phraseology is only secondary. The point I was making is that I see that EHLO/HELO validation is employed in practice, and it is in practical use. And based on my own experience, it is highly effective. Like I said, in 20+ years I've been doing strict domain validation on HELO/EHLO I do not recall a single false positive, and a mind-boggling amount of crap that got blocked. And I think that in practical situations this is going to outrank, in peoples' minds, any demand that they MUST NOT do that. > Of course, if your goal is really to discard mail for no good reason, and > you're not handling incoming mail for anyone but yourself, have at it! > Just have the decency to blackhole the mail rather than bounce it, since > you're really not doing anyone any favors. On that point I'll also have to disagree. It's better to reject the mail with a 5xx, than /dev/null it.
- [ietf-smtp] EHLO domain validation requirement in… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… John Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… John R Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… John C Klensin
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… John R Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Dave Crocker
- Re: [ietf-smtp] EHLO domain validation requiremen… Dave Crocker
- Re: [ietf-smtp] EHLO domain validation requiremen… Russ Allbery
- Re: [ietf-smtp] EHLO domain validation requiremen… John C Klensin
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Dave Crocker
- Re: [ietf-smtp] EHLO domain validation requiremen… Dave Crocker
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… John R Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… Ned Freed
- Re: [ietf-smtp] EHLO domain validation requiremen… John R Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Dave Crocker
- Re: [ietf-smtp] EHLO domain validation requiremen… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… Claus Assmann
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Dave Crocker
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… Dave Crocker
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… John Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Richard Clayton
- Re: [ietf-smtp] EHLO domain validation requiremen… Dave Crocker
- Re: [ietf-smtp] EHLO domain validation requiremen… Dave Crocker
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Laura Atkins
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Laura Atkins
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Laura Atkins
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Laura Atkins
- Re: [ietf-smtp] EHLO domain validation requiremen… John Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… Arnt Gulbrandsen
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… John Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… John R Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… John R Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… Mark Andrews
- Re: [ietf-smtp] EHLO domain validation requiremen… Mark Andrews
- Re: [ietf-smtp] EHLO domain validation requiremen… John R Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… Richard Clayton
- Re: [ietf-smtp] EHLO domain validation requiremen… Arnt Gulbrandsen
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Dave Crocker
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Dave Crocker
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… John Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… Richard Clayton
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… John Levine
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Sam Varshavchik
- Re: [ietf-smtp] EHLO domain validation requiremen… Keith Moore
- Re: [ietf-smtp] EHLO domain validation requiremen… Alessandro Vesely
- Re: [ietf-smtp] own mail server: DNS / static IP … Claus Assmann
- Re: [ietf-smtp] own mail server: DNS / static IP … John Levine
- Re: [ietf-smtp] own mail server: DNS / static IP … Claus Assmann
- Re: [ietf-smtp] own mail server: DNS / static IP … Ned Freed
- Re: [ietf-smtp] own mail server: DNS / static IP … Sam Varshavchik
- Re: [ietf-smtp] own mail server: DNS / static IP … Claus Assmann
- Re: [ietf-smtp] own mail server: DNS / static IP … Arnt Gulbrandsen
- Re: [ietf-smtp] own mail server: DNS / static IP … John Levine
- Re: [ietf-smtp] own mail server: DNS / static IP … John Levine
- Re: [ietf-smtp] own mail server: DNS / static IP … Ned Freed
- Re: [ietf-smtp] own mail server: DNS / static IP … John R Levine
- Re: [ietf-smtp] own mail server: DNS / static IP … Ned Freed
- Re: [ietf-smtp] own mail server: DNS / static IP … Dave Crocker
- Re: [ietf-smtp] own mail server: DNS / static IP … John R Levine
- Re: [ietf-smtp] own mail server: DNS / static IP … Evert Mouw
- Re: [ietf-smtp] own mail server: DNS / static IP … Sam Varshavchik
- Re: [ietf-smtp] own mail server: DNS / static IP … Claus Assmann
- Re: [ietf-smtp] own mail server: DNS / static IP … Laura Atkins
- Re: [ietf-smtp] own mail server: DNS / static IP … Sam Varshavchik