Tough-Love Message Management

A Microsoft Exchange Server administrator's list of unpleasant tasks is usually pretty long. Among these distasteful but often necessary chores is one genuine horror: policing mailbox usage. On the day when a dreaded message management task finds its way to your to-do list, you'd best be prepared.

How Big Is Too Big?
The need to manage Information Store (IS) size is inevitable because Boyle's Law also applies to email: Like gas, email data always expands to fill available storage space. Suppose your average user's mailbox size has expanded to 100MB. If you have 300 users on an Exchange Server 5.5, Enterprise Edition (Exchange 5.5/E) system, your private IS is roughly 30GB. If your backup subsystem can back up 7GB per hour, you need approximately 4 hours to perform a complete backup and 8 hours to complete a restore (restores typically take about twice as long as backups).

Is 8 hours too long? Whether shutting down an email server for a day is catastrophic or merely inconvenient depends on your environment. If your IS becomes so big that backup and restore operations become a burden to users, you have a few options for fixing the problem: You can invest in better backup hardware, move some users to another server, or migrate to Exchange 2000 Server and use its multiple databases and storage groups (SGs) to divide your backup and recovery load. But the easiest—and probably least expensive—solution to IS overload is to limit users' mailbox sizes.

The problem with mailbox size limits is that users hate them. However, you can counter users' objections with rational explanations: Limiting mailbox size might let you avoid buying more hard disks or servers, thereby saving the company money; reducing mailbox size also reduces the time the server needs to be down for restores, thereby improving user service.

Most sites that use this tough-love solution set size limits between 50MB and 100MB and increase these limits for employees whose job functions demand more mailbox space. I can't recommend a one-size-fits-all limit because users' needs and hardware capabilities vary.

Applying Mailbox Limits
After you convince your friendly population of understanding users that mailbox size limits are a good idea, the mechanics of imposing those limits are straightforward. In Exchange Server 5.5 and later, you can apply limits to individual space hogs' mailboxes or you can apply a limit to the IS.

Imposing a size limit on an individual mailbox is simple. Open Microsoft Exchange Administrator, and select the mailbox. Right-click the mailbox, and choose Properties. Go to the Limits tab, which Figure 1, page 82, shows. The Information store storage limits settings govern how large the mailbox can get before Exchange takes the following actions:

• Issue warning simply sends the user a gentle daily reminder that he or she needs to clean up his or her act. You can't modify the warnings that System Attendant sends users, although Microsoft Consulting Services will be happy to sell you customized messages.
• Prohibit send causes the IS to reject any messages the user sends. Exchange then returns a nondelivery report (NDR) to the sender. This limit is more of an annoyance than an active measure; Prohibit send doesn't keep the user from receiving mail, so the mailbox keeps growing. Also, this limit doesn't prevent users from sending mail through IMAP or POP because IMAP and POP messages usually don't go through the IS.
• Prohibit send and receive is the big daddy of limits. Users can't send or receive mail until they bring their mailboxes under the size threshold you've set. All users can do after this limit goes into effect is read (and hopefully delete) messages already in their mailboxes.