On Thu, Oct 17, 2024 at 12:37:16AM -0400, John C Klensin wrote:
> > Non-DNS question: why is the "SHOULD NOT" in paragraph 2 of 4.1.1.1
> > not a MUST NOT? What is the exception?
>
> I'll like to hear from others in the WG, but there was a certain
> reluctance to invalidate (i.e., render completely non-conforming)
> existing conforming implementations without clear evidence of harm.
> There is no harm here if servers accept it (rather than treating it
> as an error), even if they then ignore it, which is what the first
> part of the sentence essentially says. At the other extreme, SMTP
> servers are basically allowed to decline to accept a message for any
> reason(s) they find appropriate, so why should this be the exception?
> I don't have any idea how many SMTP clients do send that information
> or whether people who think market size is important would consider
> any such client worth considering.
MUST NOT (client sending) sounds right to me. To the extent that
Postfix tolerates this, the entire construct "[literal] ..." ends
up as the HELO name, including the trailing junk. But this would
typically fail the widely used "reject_invalid_hostname" restriction.
> ehlo [192.0.2.1] foo bar
< 250-...
< ...
mail from:<ietf-dane@xxxxxxxxxxxx>
250 2.1.0 Ok
rcpt to:<ietf-dane@xxxxxxxxxxxx>
501 5.5.2 <[192.0.2.1]?foo?bar>: Helo command rejected: invalid ip address
--
Viktor.
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