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Subject: Re: quota & postfix question
From: Michael Ju. Tokarev (mjttls.msk.ru)
Date: Mon Sep 11 2000 - 03:26:38 CDT

Martin McFlySr wrote:
>
> Hello postfix-userspostfix.org,
>
> I'm enable quota for mailboxes my users.
>
> Sending big message, postfix recieveing it; try deliver; cant do this.
>
> Are postfix can check size of letter before recieving?

Postfix's smtp receiver side knows nothing about mailboxes et al.

> I think, this way (without check) to DoS:
> "bad boy" get control on 5-10 hosts;
> get email address, where mailbox is full(or limited);
> wrote script:
> send email with attach, where size more then mailbox can recieved;
> run this script from his machine;
>
> and, postfix will recienig this letters, recieving, recieving....
> "traffic & CPU time for nothing", right?

There are far too many other places where "bad guys" can do this
(with postfix and with other mail software). Situation very
similar to that you described: flood of backup relay with mail
for unknown user. This can be resolved only by duplicating all
user/alias lists on backup.

> may be, it need "check of size before recieving" ?

No.

> thank you,

Regards,
 Michael.