Re: tlug: Sendmail won't deliver from unrecognized host.

[Frank Bennett <bennett@example.com>]

Rex Walters <rex@example.com> writes:

> ... I wouldn't be at all suprised if it is a sendmail
> problem, but
[snip]
> It's
> impossible to tell the problem with the limited information you've
> provided.

Looks like my wild guess was correct, though.  I had this
response privately from Michael a bit earlier:

  I changed my linuxconf.mc file to include the line 
  FEATURE(accept_unresolvable_domains)
  m4'ed it, (then removed some garbage from a buggy m4), and viola, a new
  sendmail.cf file which even accepts email from Jim Breen!! A definite
  improvement!

> Hmm.  AFAIK sendmail shouldn't be doing any DNS lookups on anything in
> the From: header.  Nor for the envelope sender, either -- the SMTP
> standard requires canonical hostnames for envelope *recipients* but not
> for senders (I don't have time to verify, but I think this is true).

It didn't have time to confirm my intuition either, but I've
since checked my facts.  At least as of 8.9.1, sendmail does run
From: headers through DNS.  Here's the relevant section from
cf/README in the sendmail 8.9.1 sources:

accept_unresolvable_domains
                Normally, MAIL FROM: commands in the SMTP session will be
                refused if the host part of the argument to MAIL FROM: cannot
                be located in the host name service (e.g., DNS).  If you are
                inside a firewall that has only a limited view of the
                Internet host name space, this could cause problems.  In this
                case you probably want to use this feature to accept all
                domains on input, even if they are unresolvable.

We'll probably see a lot more of these queries.  Anyone want to
draft up a bit of boilerplate?

Cheers,
-- 
-x80
Frank G Bennett, Jr         @@
Faculty of Law, Nagoya Univ () email: bennett@example.com
Tel: +81[(0)52]789-2239     () WWW:   http://rumple.soas.ac.uk/~bennett/
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