Stop Sendmail from bouncing unknown user?

[paddy]

On Wed, Jan 05, 2005 at 06:46:33AM +0000, Brian Lewis wrote:
> I would like to configure Sendmail outgoing to not generate a 'bounce
> reply' if the target user is 'unknown or invalid'.

IMHO, this is the ideal configuration: bounces are a nuisance if they
don't go to the right place.  But, I'm sure you also have in mind the
purpose of bounces.

> Basically if Sendmail
> Outgoing is unable to deliver it then it should keep attempting to
> deliver, but if its told by the receiving server the user doesn't exist

If you don't attempt delivery before you reply then this is already
too late, IMO.

(Now, if the receiving server said 'we don't want it, its spam' ...)

> then I don't want it to reply back to the spammer that it doesn't exist,
> instead it should just discard the email.

Au contraire.  I think:

If you're really sure that its spam, by a process equivalent to delivery,
then you can, with your 'agent of the user' hat on, rather than your 'MTA'
hat on, justify dropping the mail on the floor - thereby robbing the
spammer of valuable feedback, and saving your resources.

I would suggest that to act as the 'agent of the user' should be an
explicit arangement, and that this deviation from normal MTA behaviour
be explicitly understood as part of that arrangement.

rfc2821 seems quite clear on this point:

   If an SMTP server has accepted the task of relaying the mail and
   later finds that the destination is incorrect or that the mail cannot
   be delivered for some other reason, then it MUST construct an
   "undeliverable mail" notification message and send it to the
   originator of the undeliverable mail (as indicated by the reverse-
   path).

I can't find the 'get-out clause' that relieves you of this obligation
in general, although I do not profess to have a good knowledge of
all the relevant standards.

> Anyone know if Sendmail can be configured in this way?

See the other postings.  ldap or milter-ahead.

I would suggest that having a method that does require you to accept
(or at least minimizes) mail that later you find you cannot deliver
because the destination is incorrect, will give you more freedom in
your choices about when to silently drop undesirable mail.

Can anyone point out a circumstance in which this is simply
technically impossible to acheive ?

> Sick of seeing the server attempt to delivery
> thousands of invalid or unknown user replies usually to invalid FROM
> addresses.

You have my sympathy, really.

Regards,
Paddy
--
Perl 6 will give you the big knob. -- Larry Wall

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