Pop3 multiple emails

We are running Domino 6.0.2 cf1 on iSeries v5r2.Many of my users access their mail by POP3, using the Outlook Express client.

For one user, he often recieves emails multiple times, but one time per connection. He has gotten the same email up to 4 times.

His outlook express is set to NOT leave email on the server.

What can I do to fix this?

Thanks,

Jim