If the user exceeds their quota, then warnings will continue to be sent, but the user will be unable to send mail. The user can still receive mail, but must reduce the size of the mailbox below quota, before they will be able to send mail again. Then select the Compose menu, and click on the 'New Information Store Usage Query' option. Extra quota is available at 15 pounds per year per 50000KB, and for students this quota maybe spread among accounts by a department.
Extra quota is obtained by submitting a request via the help desk.