RFC: Check mail quota at a mail relay (backscatter)

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RFC: Check mail quota at a mail relay (backscat...
\ Jozsef Kadlecsik (5 May 2008)
. \ mouss (5 May 2008)
. . \ Jozsef Kadlecsik (6 May 2008)
. . . \ mouss (6 May 2008)
. \ (HAKNER J) (5 May 2008)
. \ (Wietse Venema) (5 May 2008)
. . \ Jozsef Kadlecsik (6 May 2008)
. . . \ (Wietse Venema) (6 May 2008)
. . . . \ Jozsef Kadlecsik (7 May 2008)

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Subject:	RFC: Check mail quota at a mail relay (backscatter)
Group:	Postfix-users
From:	Jozsef Kadlecsik
Date:	5 May 2008

Hi,

I'd like to prevent to generate bounces at a mail relay due to the
recipient being over the mailbox size limit or quota at the next-hop
destination machine.

Is there a way/would it be feasible to design a Postfix service, which
could be called to query the next-hop destination *before* accepting the
mail? It could be a standard SMTP client issuing always

MAIL FROM:<foo@src> SIZE=xxx
RCPT TO:<bar@dst>

To err on the safe side, let's assume that the restriction corresponding
to the service actually executed if it is called

- from the smtpd_sender|recipient_restrictions and SIZE was announced,
- from the smtpd_data_restriction and SIZE was not announced and
the message has got a single recipient.

Assuming that the queried next-hop destinations run Postfix as well (;-),
we'd need another service to connect to, which could be a combined simple
smtpd & enhanced local service answering the question whether the message
would fit into the mailbox or disk quota of the recipient.

What do you think? Is it too complicated?

Best regards,
Jozsef
-
E-mail : kadlec, kadlec
PGP key : http://www.kfki.hu/~kadlec/pgp_public_key.txt
Address : KFKI Research Institute for Particle and Nuclear Physics
H-1525 Budapest 114, POB. 49, Hungary