Since by default, the IMAP protocol leaves mail on the server, you should check your quota periodically to make sure you are within limits. Once you've freed up some space, you will be able to receive incoming messages, however this might not be immediate. It may take anywhere from 15 minutes to a couple of hours before you begin to receive incoming e-mail again. See Tips for managing your quota for suggestions on how to stay within quota. Tips for managing your quota Move e-mail attachments you've received to your local machine or Athena directory and delete them from the post office server.
Attachments can be large and take up space.
Go through your messages stored on the post office server regularly and delete those you no longer need. You may want to devise an archiving strategy to make it easy to find messages that can be deleted. If you have stored messages that you access infrequently, move them to your local machine and delete them off of the post office server. If you set up a mailbox to store copies of messages you've sent, be sure to go through it regularly to delete ones you don't need, or move them to your local machine for long-term storage.