[Exim] Problems interworking with Exchange 2000

We're having a few problems interworking with Microsoft Exchange 2000.
This is set up to use our exim mail hub as a smarthost (bham.ac.uk).
A problem then ocurrs when trying to receive email. The following
message appears in the logs

17Um1g-0004B7-00 SMTP data timeout (message abandoned) on connection from is1.bham.ac.uk (is1.adf.bham.ac.uk) [147.188.129.77]

Has anyone seen anything similar or got any suggestions for what
may be going wrong/how to fix it? (a skip for the 2000 servers
is not an option).

Chris Bayliss