Re: MTA or SMTP proxy?

Gábor Lénárt:
> Hei,
> 
> Recently I am thinking of reimplementing our MX servers. Of course rcpt
> check is a must, also I should not generate NDRs later, I should only accept
> mails from outside which won't cause bounce on the mail store MTA later. My
> problem: there are some conditions cannot be forecasted easily, I can't be
> sure that mail can be delivered (over quota, user is deleted between the
> moments of mail at MX and the mail storage etc). Some people would say, that
> this issue is minor, and quite rare so I should not care about this. However

Perhaps you can use an access map (plain file or perhaps *SQL) with
"reject" actions for over-quote users. These tables don't need to
be updated yby the minute.

/etc/postfix/main.cf:
    smtpd_recipient_restrictions = 
	... hash:/etc/postfix/recipient_access ...

/etc/postfix/recipient_access:
    user1 <at> example.com 	450 4.2.2 User mailbox over quota
    user2 <at> example.com 	450 4.2.2 User mailbox over quota

It could also done with "reject_unverified_recipient" provided that
the mailbox delivery system reports over-quote conditions.

> Also the over quota problem is solved. Also, I hate when there is some rare
> problem with the backend mail servers (mail stores) and we have huge queues
> filled up with waiting mails, I would say, that MX servers shouldn't accept
> anything if they are not 100% sure that they can transfer the mail to the

This could be done with a wild-card
access action:

/etc/postfix/main.cf:
    smtpd_recipient_restrictions = 
	regexp:/etc/postfix/down.regexp

/etc/postfix/down.regexp:
    /./	450 4.3.2 System not accepting network messages

It could also done with "reject_unverified_recipient" if the bottle
neck is directly down-stream. reject_unverified_recipient does not
work across multiple hops.

	Wietse