Re-authenticate using dialup and offline folders

[Juergen]

I'm using Office XP, Windows XP and offline folders on the clients. Exchange
5.5 is used on the mail servers. User are connecting through dialup to our
network. When they start synchronizing with the mail servers, they have to
logon again to the domain again, although they are already logged on to the
domain and PASSWORD AUTHENTICATION is used. If we are downgrading the client
to Outlook 2000, the problem does no longer exist.
Does anyone have an idea?

Thanks

Juergen