Outlook Still Running After Exiting

[Andrew]

I'm using Outlook XP as my email client, when I leave the
office I exit Outlook so it won't be running and
receiving email, allowing me to check email remotely via
webmail interface. However I've noticed that I get no new
messages when doing this webmail checking, as Outlook is
somehow still receiving the email even though it is not
running (but the computer is still on).

Any ideas how to stop Outlook checking and receiving new
email messages when it shouldn't be running?

Many thanks - Andrew