Outlook as pop3 having slowdown issues

We have a user running Microsoft Outlook 2003 as a POP3 client. Every once and awhile his outlook gets an icon in the systray with the message ?Microsoft Office Outlook is synchronizing folders?. When this happens Outlook grinds to a halt. He can receive mail but not send it out. Everything I have found thus far discusses Exchange and MAPI clients. Since he is configured as a POP3 client I have no options for Synchronization or Caching folders.

We have two other users that also are setup with POP3 access and they don’t ever recall having that issue so i believe it has to do with his computer or setup but it’s the same as the other two users.

Any ideas on how to turn this off or what the cause of the slowdown is?