In Outlook, from the
Tools menu, choose
Mailbox Cleanup
Click on the
View Mailbox Size button. You'll see the total size of the mailbox and individual mail folders.
Outlook 2010
In Outlook, From the
File
tab, under
Info, select
Cleanup Tools, then
Mailbox Cleanup...
Click the
View Mailbox Size... button
Select the
Server Data tab of the Folder Size window.
Note: Be sure to look at the
Server
tab, not the
Local
tab. The size of your folders listed on Local do not count towards your email storage quota, since these files are being stored on your 'local' hard drive.