Mailing List Archive

Message sizes are wrong
I see this in my (not Exim) SMTP server logs.

A friend's Exim system says it's going to send me a 7124 byte message,
but the message it sends using BDAT is actually 6001 bytes. I got the
message, it's fine, the 6001 bytes is right. This seems fairly
consistent among Exim systems that send me mail. The 6489 in the next line
includes the Received and Authentication-Results headers added locally.

It's hardly a crisis, but it seems strange.

R's,
John



2021-04-09 07:44:55.348285500 mailfront[57623]: HELO x.x.net
2021-04-09 07:44:55.403838500 mailfront[57623]: MAIL FROM:<dave@x.net> SIZE=7124
2021-04-09 07:44:55.645717500 mailfront[57623]: RCPT TO:<johnl@taugh.com>
2021-04-09 07:44:55.648413500 mailfront[57623]: 2.3.0 Got 6001 octets.
2021-04-09 07:44:56.890727500 mailfront[57623]: 2.6.0 Accepted message qp 57627 bytes 6489
2021-04-09 07:44:56.916122500 mailfront[57623]: bytes in: 6116 bytes out: 345
2021-04-09 07:44:56.917293500 tcpserver: end 57623 status 0

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Re: Message sizes are wrong [ In reply to ]
On 09/04/2021 17:19, John Levine via Exim-users wrote:
> 2021-04-09 07:44:55.348285500 mailfront[57623]: HELO x.x.net
> 2021-04-09 07:44:55.403838500 mailfront[57623]: MAIL FROM:<dave@x.net> SIZE=7124
> 2021-04-09 07:44:55.645717500 mailfront[57623]: RCPT TO:<johnl@taugh.com>
> 2021-04-09 07:44:55.648413500 mailfront[57623]: 2.3.0 Got 6001 octets.
> 2021-04-09 07:44:56.890727500 mailfront[57623]: 2.6.0 Accepted message qp 57627 bytes 6489
> 2021-04-09 07:44:56.916122500 mailfront[57623]: bytes in: 6116 bytes out: 345
> 2021-04-09 07:44:56.917293500 tcpserver: end 57623 status 0

Expected. Exim does not have perfect information about the final
message size at the time it has to send the MAIL FROM, not
having finished constructing headers by then.
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Cheers,
Jeremy

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Re: Message sizes are wrong [ In reply to ]
On Fri, 9 Apr 2021, John C Klensin wrote:
>> A friend's Exim system says it's going to send me a 7124 byte
>> message, but the message it sends using BDAT is actually 6001

> (1) I can't guess whether this is the source of the problem but,
> depending on how an MTA is organized, trying to avoid extensive
> look-ahead, etc., making an estimate and rounding up seems
> operationally sensible now matter what the spec says.
>
> (2) The intention with SIZE was always to specify a maximum. ...

Oh, sure. If the size were slightly higher than the real amount that
would make sense but they are often wildly different.

FWIW, Microsoft is even worse, SIZE=18944, actual size 9543, or
SIZE=18979/9547, or SIZE=70805/44046, or SIZE=24664/12416.

Some other senders like Google consistently send SIZE that exactly matches
the message size.

Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly

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Re: Message sizes are wrong [ In reply to ]
On 09/04/2021 22:19, John R. Levine via Exim-users wrote:
> Oh, sure.  If the size were slightly higher than the real amount that would make sense but they are often wildly different.

Exim provides a "transport option" tunable for the increment
over the base message size, to allow for headers yet to be added
by the transport and/or any manipulation done by an external
transport-filter. Naturally, this is handing rope to admins.
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Cheers,
Jeremy

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