The default quota for accounts on Exchange 2010 is 4GB. You can view your quota usage at any time, as described below.

Outlook 2010

  1. Click on the File tab and, if necessary, Info.
  2. Under Mailbox Cleanup you’ll see your current use of the mailbox.

Outlook

Outlook 2011

  1. Do a right-click on your Exchange mailbox in your Mail Folders list
  2. Select Folder Properties
  3. Click on the Storage tab to see your overall quota and use by each folder

OWA
Login to xmail.bu.edu. On the main Mail page, move your mouse to hover over your name (in the left column).  A pop-up will then display how much space you are using and what your quota is.

Outlook 2007
Go to Tools -> Mailbox Cleanup ->View Mailbox Size