[Dovecot] Why deliver+usercheck? deliver+MTA?

[Jerry]

On Wed, 13 Oct 2010 11:32:50 +0200
Lukas Haase <lukashaase at gmx.at> articulated:

> Hi,
> 
> I successfully configured dovecot using virtual users (and LDAP/AD). 
> deliver is the LDA and verifies if the user exists (as recommended in 
> the WIKI).
> 
> However, the howtos in the Wiki say *nothing* about the case that the 
> recipients should be verified *before* receiving the messages
> (prevent backscatter, ...). All configurations in the dovecot-Wiki
> (postfix and exim) just accept the mails and pass them to deliver.
> Also, all howtos which I found on the web. If the user does not
> exist, the mail is bounced because the mail was already accepted by
> the MTA. Nowadays this is an unacceptable configuration!
> 
> Is there a special reason why there is no discussion about this?
> 
> However, as postfix seems to be really too unflexible I have set up
> exim to handle incoming mail and do the usercheck in the router (with
> an LDAP query). But now the user is doubled-checked: Once when
> receiving with exim and a second time in deliver. This is not
> necessary, so I guess I can disable the LDAP query for deliver and
> set up a static userdb.
> 
> Why does the Wiki recommened to verfify with deliver when the user
> needs to be checked at the MTA anyway?

First of all, I totally disagree about your Postfix comments. I have
personally found it to be rather easy to configure, and totally RTF
compliant, unlike some other MTAs. In any case, only the MTA can bounce
mail without causing back-scatter. Postfix has checks in place to check
and reject or accept mail. It is not Dovecot's job to do so. By the
time Dovecot receives the message the recipient should have all ready
been verified.

-- 
Jerry ✌
Dovecot.user at seibercom.net

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