[Exim] Bandwidth problem.

Hi.

This is somewhat off topic, I know.

I'm having a problem with bandwidth for SMTP traffic to and from certain hosts.
It manifests itself as a sharp drop in transfer rate after about 200kB, down
from the regular maximum transfer rate of that connection to about 4kB/s.

I've tried running various different services on port 25, so it isn't exim.

I _don't_ see the same problem for ssh and web traffic.

It only appears to happen between hosts that are far (in hops) apart, for
instance between Mexico and Norway.

Large mails are timing out, and travelling users using smtp-auth are having
problems.

Is this something anyone here is familiar with? Is it perhaps some common
spamworm counter measure?

--
Daniel Mikkelsen
Copyleft Software AS