MS Exchange Server, how to manage it?

If you look @ the properties of your users in the Exchange, you'll find in one of the Tabs an option to restrict the amount of space used by the users.
One is for an warning which will be issued when the users reachs the limit. After that, if the user don't cleanup their email box. The email account will be lookout and only the administrator can unlock.
You can select multiple users @ 1 time and apply the same rule simoutaneously, by holding down Ctrl key and click on all the users that will need changes @ one time and then select propertis from right-click or menu.

Good Luck!

it's much quicker to put the limit on the infromation store instead of doing it by indivual users. from your admin console select the server then the private information store object right click then select proprities and set your limits on the store through the general tab
hope this helps

A good policy is to set a limit on the information store as mentioned above. This is done on the Information Store properties page. Then, at each user's mailbox, they should be set to use the IS defaults (I believe this is on the Advanced tab in the mailbox properties). You can override the IS defaults if needed for specific users by entering specific limits in the mailbox properties rather than checking "use IS limits". As far as policy goes, you need to work out with your company management a balance between the storage needs of users and the storage available on your server. When you set storage limits, you are going to force your users to delete email or use archive files. If users have a real (or even really imagined) need to save information, they will start archiving, and this eats up disk drive space, too. My opinion, frankly, is that hard disk space is cheap if you have a real business need to store more information. But it needs to be managed well, too. Hope this helps.