If Outlook express is running and set to send / receive every so many
minutes that will be the likely cause.
Go tools>accounts and click on both news and mail tabs in the window that
appears (Especially mail)
On the right next to each account name you should see any available listed
under "Connections"
I bet under there for at least one of them is an old dial up ISP name.
Double click on any account names like that and when their properties
windows appear hit the "Connection" tab and uncheck the box for "Always
connect using".
All being well the problem will go away.
If not this it could be something like Antivirus searching for updates etc.
Like OE they have no way of knowing how you are connected so if in the past
a direct connection through a dial up ISP was specified they would have to
disconnect and redial to get the right network. The reason OE is specific
like this is because most ISP will only permit using their mail servers for
sending if you are on their network, so if you had two dial up accounts your
mail accounts would show errors if you tried to use A's email account while
connected to B.
Charlie