> >The SMTP client "MUST" send the canonical hostname for its source
> >
> > Blimey, where does it say that?
> > :-)
>
> RFC 2821, section 3.6:
>
> and in section 4.1.4:
Thank you.
And thank you also to Greg Woods for
> RFC 1123 section 5.2.5, if you must know.... :-)
And ...
On Thu, 1 Nov 2001 Philip Hazel wrote:
> Even though the word MUST does not appear, I believe that is the
>intention of this wording:
>
> The argument field contains the fully-qualified domain name
> of the SMTP client if one is available.
>
>It then applies the weaker SHOULD for what should happen if there is no
>name available.
For some reason RFC 2821 holds back from saying 'MUST'.
I guess there may be some elbow room intended for some wierd
situations - I don't think they just throw these RFCs together.
I suppose a 'bad' client could point to it as justification.
Incidentally, 2821 is clearly intended to replace
1123 (as far as mail transport goes) - but that would be a
standardization issue (?).
I'm not suggesting that there's any explicit support in any RFC
for a client NOT giving its canonical hostname (or IP literal) in HELO.
It's just that there's scope for a really nasty "is / isn't rfc-legal"
argument if you turn down transactions just because you don't like the
HELO argument. Also, I can't see how any policy based on this data
couldn't be better realised in other ways.
I'd say that Peter Radcliffe probably got it about right
when he gave the list:
> HELO/EHLO isn't reliable. No one with any sense cares about the name
> provided.
Exim, which is a very sensible piece of software, has helo_verify
unset by default, but of course, it's there if you MUST :-)
--
all the best to you and yours ...
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