[exim] SMTP data timeout problems...

So, I looked around and found documentation about the following messages:

2007-11-27 15:47:01 SMTP data timeout (message abandoned) on connection
from smtp04.newegg.com [216.52.208.142] F=<jshatch@???>
2007-11-27 15:49:09 SMTP data timeout (message abandoned) on connection
from smtp04.newegg.com [216.52.208.142] F=<jshatch@???>
2007-11-27 15:56:07 SMTP data timeout (message abandoned) on connection
from smtp04.newegg.com [216.52.208.142] F=<info@???>

and others like them (currently I have 4404 of these messages in my
current log). The documentation I found said that it is likely an MTU
problem with my router (I am on an ADSL line). It said to try reducing
the MTU from the default (1492) to something like 1300. I tried that,
as well as 746 and the minimum allowed on my router, which is 546. All
of these values do the same thing.

Does anyone else have any other ideas to try?

The router is a Linksys WRT54G running DD-WRT. My ADSL modem is a Cisco
678 running in bridging mode.

Thanks.

Jarom