Re: at what stage is message_size_limit applied?

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at what stage is message_size_limit applied?
\ Mike Kenny (14 May 2007)
. \ Victor Duchovni (14 May 2007)
. . \ Mike Kenny (14 May 2007)

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Subject:	Re: at what stage is message_size_limit applied?
Group:	Postfix-users
From:	Mike Kenny
Date:	14 May 2007

Thanks Victor. This is useful information.

On 5/14/07, Victor Duchovni <Victor.Duchovni> wrote:
>
> On Mon, May 14, 2007 at 07:45:59AM +0200, Mike Kenny wrote:
>
> > The subject says it all, I hope.
> >
> > I have a client complaining that he is being billed for bandwidth due to
> > attempting to send a mail that exceeds our maximum size. His argument is
> > that as we did not send the mail for him, he should not be billed for
> the
> > bandwidth. My question is 'is this restriction, message_size_limit,
> applied
> > during the handshake or is it dependent on counting the bytes received?
> i.e.
> > in the first case, the client would not have used the bandwidth, in the
> > second he would have. I need to get back to him and explain what he used
> and
> > what he was billed for.
> >
> > (the client is not being very cooperative in providing supporting
> > information to assist me in locating the fault. this is why I am
> > investigating postfix behaviour rather than log contents)
>
> Postfix tells ESMTP clients (most are these days) the maximum message
> size it is willing to accept. Many (but not all) ESMTP clients will not
> send messages larger than the advertised limit.
>
> - In many cases trasmission is avoided when the client fully
> supports ESMTP "SIZE".
>
> - In some cases clients don't use ESMTP or ignore "SIZE" and
> send anyway. Overly large messages are rejected at ".".
>
> - In some very rare cases, the client sends a message just under the
> limit, but it is rejected at "." because queue file overhead pushes
> it just over the limit.
>
> Sane contracts are either flat-rate or bill for bandwidth used, regardless
> of whether any benefit was derived from said use, with possible DoS
> attack exemptions.
>
> --
> Viktor.
>
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