[Dovecot] Re: LDA Questions

[John Peacock]

Timo Sirainen wrote:
> In any case that requires calling the LDA immediately after the mail is
> received. I thought people didn't like to do that because if there are
> slow spam checks and such the incoming SMTP connection pool could
> quickly fill up and new SMTP connections would get rejected.

An LDA should only be called as a terminal case (i.e. all SMTP transactions have
been closed and the message has been queued for local delivery).  Any error at
this point should either be temporary (over quota?) or permanent (something very
wrong in the configuration, i.e. a message was accepted when it shouldn't have
been).  In the former case, the MTA should requeue the message for later
delivery (no harm, no foul), and in the latter, the MTA should bounce the
message back to the envelope sender.

IMNSHO, an MTA (e.g. postfix, qmail, etc) that wishes to refuse messages due to
quota concerns should *not* rely on an external LDA to do that calculation.  If
you want to have that behavior, you need to use whatever built-in capabilities
for that existing in the MTA.  It is much more important for the local delivery
to be decoupled from the SMTP transaction, precisely because of the possible
need for timeconsuming message scanning.  Of course, in practice, I always scan
my messages for viruses during the SMTP transaction, since I refuse to generate
bounce messages for those (which is the inevitable result of performing scans
during local delivery).

John

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John Peacock
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