The way that the IIT e-mail system is set up is that when you check you e-mails and click the delete button the e-mails are actually not deleted; they are sent into your 'Trash' folder to be later deleted when you are sure that you want them permanently and finally deleted. Emails in your 'Trash' folder still count against the maximum space you are allowed on the email server.

WARNING: This will permanently and finally delete all of your e-mails in your 'Trash' folder. Everytime before you do this, I suggest that you take a quick and cursory look through the e-mails to make sure that you don't and will not need any of them again or that you have backed up all of the important ones. Once your trash folder is emptied, your space used will decrease and, as a result, you will have more room for new e-mails.

If your 'Trash' folder is empty and you still have problems, it may be that you're saving a copy of all the messages you have sent, and that is causing your mailbox to fill up. Please see this page to check if you're saving a copy of outgoing mail.