email storage usage exceeded 2G

I have been receing this email message every day this week even after I go in and delete tons of email. i get it down belwo 2G and then the next day it is way over 2G. What in the world is causing this??? 

Your mailbox is approaching its quota.

Please delete some messages from your mailbox!

Be sure to check all subfolders such as Trash, SentMail and any folders you have created.

If you do not delete some of these messages soon, you will not be able to send or receive any more messages.

For more information, please contact customer support or visit http://support.cox.net/