Since mailbox quotas are necessary, it is important to take active steps to manage your mailbox. (Current quota allocations: 250 MB for students, 1 GB for faculty/staff)
Determining Mailbox Size
To view the total size of your mailbox, right-click over your mailbox and select Properties for Mailbox.... Click the Folder Size button in the lower left hand side of the Properties dialog box. A secondary dialog box will be displayed that shows the total size of your mailbox as well as the sizes of each individual folder. These sizes are expressed in KB, and 1 GB equals approximately 1,000,000 KB.
Delete or archive items in the Sent Folder
Outlook automatically retains a copy of all your outgoing messages. You can sort by size, date or other parameters to help you determine which messages, if any, to keep. To delete messages from this folder, simply select it and delete messages as you would for any other folder. You can select multiple messages to delete at once by using Ctrl + click or Shift + click. You will have to empty these messages from your deleted items folder
Outlook does offer Auto-Archiving, but we strongly recommend against using this feature. Instead, we recommend storing your messages in personal folders to help reduce your mailbox size.
Empty your Deleted Items folder
Emails that you mark deleted are not deleted automatically. Instead they go into your Deleted Items folder. As with sent messages, you can sort by size, date or other parameters to help you determine which messages, if any, to keep. These messages also can be stored in personal folders.
If you are comfortable permanently deleting all items from this mailbox, simply right-click over the Deleted Items folder and select Empty "Deleted Items" Folder. It is possible to recover deleted messages for up to 7 days. After that, messages are permanently deleted, and they cannot be recovered.