This is for my in-laws, so the description of the problem is second hand.

They use SBCYahoo DSL and an SBC provided DSL modem. A Dlink wireless
router is connected to the modem. A desktop is wired to the router, and
a wireless laptop is also used. This was all set up about 10 weeks ago.
Both pcs use XPHome and OE. Both OEs are set to leave messages on the
SBCglobalnet server so they can download all messages from either pc.
They have not yet deleted any messages from the server.

Here's the problem:

Whenever they collect email on the laptop (I think it's only happening on
the laptop, I have to check with them), OE says downloading 1, 2, 3, etc.
messages of 300 (or more). The older messages are not actually
downloaded, only the new ones.

Could this be a corrupt .dbx file in OE on the laptop?

Is this peculiar to SBCYahoo DSL?

They also have their McAfee set to check outgoing email for viruses.
Could this be the problem. I'm grasping at straws at this point.

Thanks.