So, I've noticed that there are quiet a few people on here who post something along the lines of "My message box is full" or "I've reached my limit" in reference to their mail box on their profile. I'm here to inform all who might not know, you can delete past messages and free up more room! Surprise! Right? :D
You can do this by following this path:
And then check the box beside the messages you want to delete, click on the drop down box at the bottom of the page, click "Delete Messages" option and then "Move Messages."
This will allow to to send and receive messages and also should reduce the number of people who delete and recreate accounts for the sake of mail.