When you add an employee, you also add a mailbox to the Exchange 5.5 information store. And the store gets bigger. If you're still using 5.5, you probably know that -- unlike earlier versions of Exchange -- the information store size of Exchange 5.5 essentially has no limit. The only limit really is the amount of disk space available on the Exchange server.
Exchange will help you out with warnings that you're getting close to that limit. As disk space gets smaller a message appears in the event log informing you of how much disk space remains. You may also notice slow disk performance, especially when trying to examine the disk in explorer.
Once the disk has reached its limit, when users try to add data to the store, they may get the following error message: "Network problems are preventing connection to the Microsoft Exchange Server." Exchange stops the information store service and the transaction logs will then hold the data for messages that cannot be added to the store.
So how can you get your Exchange server up and running after encountering a problem like this? Here are a couple suggestions. First, try setting up another Exchange server and move some mailboxes to that server. And you can look at mailbox resources and delete unused ones; those whose users have left the company, common mailboxes that are no longer in use, etc. And you should have a policy, enforced, that users with large mailboxes move some of their large files to their workstations' hard drives.
It's a good idea to do this on an ongoing basis, so that you don't get the user errors. And once you performed these cleanup exercises, perform an offline defrag of the Exchange database using the eseutil /d /ispriv command. This will be able to reduce the information store size, and you will reclaim some hard drive space.
Adesh Rampat has 10 years experience with network and IT administration. He is a member of the Association Of Internet Professionals, the Institute For Network Professionals, and the International Webmasters Association. He has also lectured extensively on a variety of topics.