The more mailbox space used, the more application pauses you may experience while you perform typical operations in Outlook. These typical operations include reading, moving, deleting and composing email messages.
Following are some tips for reducing your mailbox usage size:
Email links rather than attachments
Instead of emailing shared documents as attachments, store them on a shared drive and email the link.
Archive your email using the Export Exchange Mailbox tool. Once the mail has been successfully archived it can then be removed from your mailbox.
Delete anything you do not need
Over time the Deleted and Sent items folders usually fill up with a large number of messages. It is good to periodically go through these folders and clear out messages you no longer need. If the messages are important and need to be kept, move them to another folder and delete the rest.
Setup a shared mailbox
Do you have a lot of shared mail? Do many people in your workgroup receive common mail from a distribution list? For example, your area may be subscribed to a distribution list where many people receive the same copy of a message in their mailbox. This puts extra load on the server and your own personal Outlook. It is far more efficient to request for a shared mailbox to be setup. This allows all the mail to be in one place and centrally managed.
Setup rules to automatically filter mail into different folders. For example, you may get a lot of mail from a certain email address. A rule could be setup to move this mail into its own specific folder automatically which will stop it filling your Inbox.