It could be that you have run out of quota on your Email-Unix filestore (T: drive).

If you are a WTS user you can check this by going to Start > Programs > Software P-R > Quota Usage

Alternatively, log in to the online quota checking web page, click on your status (student/staff), and your current quota will be displayed.

If you find that you have run out of quota, you will need to delete some files from your Email-Unix filestore. You can do so by deleting messages and attachments that you no longer need.

If your quota is not the cause of the problem, then contact the ISD Service Desk who can advise further.