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Re: Compressing Mail Transfer

On Thu, Nov 08, 2001 at 04:52:03PM +1100, Andrew Tait wrote:
> I was wondering if anyone has come across a way to compress the SMTP
> transfer of mail between two servers to reduce bandwidth usage.
> The situation we have is a mail server that is dialled into out
> network, and a mail server at our border connection. At the moment,
> the dial-up server is sending mail directly out. I would like the
> dial-up server to send the mail to our main mail server instead (as
> easy as pie to do!), but would like to compress the mail transfer
> between the two, as the dial-up server has a limited connection.

there are several ways of doing this. including:

1. run a compressed tunnel between the two machines and set up the
transport table and/or smarthost/relayhost configuration so that the
smtp connection goes over the tunnel.

there are several tunneling programs available. vtun is one of the
better ones, it supports both encryption and compression of the tunnel's
traffic, and it works with most unixes incl. linux, freebsd, and
solaris. see http://vtun.sourceforge.net/ for details.

2. alternatively, use uucp (you can use stunnel & openssl to ensure that
the uucp connection is encrypted and compressed).

3. if you've got a good grasp of how internet mail works and how
your MTA works then it's not that difficult to construct a custom
batched-smtp scheme using ssh and some shell scripts. you can either
use gzip to explicitly compress the mail batches (better compression)
or simply rely on the compression built-in to ssh (slightly easier
to implement). the drawback here is that this is, to some extent,
re-inventing uucp.


craig sanders <cas@taz.net.au>

Fabricati Diem, PVNC.
 -- motto of the Ankh-Morpork City Watch

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