For security reasons you will automatically be signed out of Webmail if you are inactive.
This feature is designed to ensure that you don't forget to sign out of your account. It helps keep you and your account safe.
Once Webmail deems that you have been inactive a warning pop up will appear on your screen. To avoid being signed out of your account select OK before the 30 second timer expires. If you have already been signed out you can sign in again using your credentials.