How to clean a full mailbox
Begin by right clicking your inbox.

After finding where the bulk of your space is being used you can decide how best to shrink your mailbox.
Here are some suggestions for freeing up space:
- Clean out your RSS Feeds folder
- Empty your Deleted Items folder
- Clean out unneeded items in your Sent Items folder
- Archive old emails that you want to keep on your local computer
Go here for instructions on archiving