- delete all your sent items
- get rid of large attachments by saving them to your computer then delete the email
- delete everything in your spam folder
- Finally empty your trash folder.
I have been getting a number of bounce backs, particularly from optusnet accounts indicating the user's mailbox is full. That could be because the in-box itself is full or if your trash file has not been emptied in a long while, same same for your sent items file. Soooooo;