Moving Mailboxes Between Servers

Computing environments change all the time. Systems administrators add hardware and software, and users move among servers. Network administrators must take these facts in stride and accommodate change when necessary. Therefore, Microsoft Exchange Server administrators need to know how to move user mailboxes. Exchange Administrator makes moving mailboxes between servers in the same site a breeze, but the process of moving mailboxes between servers in different sites requires manual work. Like any task that involves manual intervention, moving mailboxes between sites opens up the possibility that administrators might make a mistake—for example, forgetting to update distribution lists or permissions on a public folder. Moving mailboxes between sites can be so problematic that some system designers reduce the number of sites in an Exchange organization if they know that the organization's user population is prone to move between offices. Fortunately, several tools can help you move mailboxes within and between sites.

Why Move Mailboxes?
Administrators typically assign user mailboxes to servers according to the users' work groups. This organizational design takes advantage of the old 80/20 rule for email, which predicts that 80 percent of a user's messages go to recipients within the user's primary work group and only 20 percent of a user's messages have recipients outside the user's work group. This ratio obviously varies among companies, but most users send most of their messages to people they work closely with.

If the 80/20 rule describes many of your users, keeping users who are in the same work group on one server saves storage space on your server and reduces network activity. Exchange Server uses the single-instance storage model to save messages with multiple recipients on the same server—Exchange Server stores one copy of the messages' content and attachments, and the recipient mailboxes access the content and attachments via a system of pointers. When a user sends a message to multiple recipients, Exchange Server sets the message's reference count to the number of mailboxes with pointers to the message. When the user of one mailbox deletes the shared message, Exchange Server decrements the message's reference count by one. When the reference count reaches zero, the Information Store (IS) removes the content from the database. If one server holds mailboxes for all a message's recipients, the message takes up a minimal amount of space in your servers' ISs. The smaller your ISs, the less time you'll need to spend backing up your systems and performing other administrative activities. Therefore, if most of your users send messages primarily to members of their work group, you'll save time and money by keeping users in each work group on the same server.

In addition, making sure users' mailboxes are on the same server as mailboxes for the rest of their work group can reduce network traffic. The IS delivers messages to mailboxes on the same server as the sender's mailbox, so Exchange Server doesn't route those messages through the network. The Message Transfer Agent (MTA) must handle messages that users send off the server, so those messages generate network traffic.

Finally, if users physically move to a new location, leaving the users' mailboxes on their current server might require the users to have an extended network connection to their mailboxes. Such an extended network connection generates network traffic every time users check their inboxes, and the users experience slower response from Exchange Server than they would experience if their server was nearby. Users don't care about extra network traffic, but they tend to hate anything that slows response.

For these reasons, moving mailboxes to increase the number of messages that the mailboxes can share might be a good idea for your organization. However, before you move any mailboxes, think about whether you really need to move them. Moving mailboxes has a few disadvantages. First, moving mailboxes takes time. Second, when you move a mailbox off its current server, you lose the efficiency of the single-instance storage of any messages the mailbox shares with other mailboxes on its current server. Third, when you move mailboxes, the mailboxes' users temporarily lose email service.

Exchange implementations vary greatly. Avoiding mailbox moves is probably a good tactic if your servers hold thousands of user mailboxes in a centralized environment. But if you have users distributed in small groups across the country, moving mailboxes might be a good idea, because providing fast service usually requires users to be close to the server that hosts their mailboxes.

The Move Mailbox Function
If you decide to move mailboxes from one server to another within the same site, you can do so easily. Select one or more mailboxes from the list of the server's recipients in Exchange Administrator, then click Tools, Move Mailbox. Exchange Server will prompt you with a list of servers in the site. Select the server you want to move the mailboxes to, and click OK to start the move.

When you move mailboxes, messages and other items such as e-forms and attachments must move between servers. Exchange Administrator uses standard Messaging API (MAPI) remote procedure calls (RPCs) to transfer these mailbox items; Exchange Server transfers the data as a stream of messages to the target server that continues until the transfer completes.

Exchange Server treats the data transfer like it treats every other insertion into the IS, so the target server's transaction logs report the traffic. This logging means that if each of your logs is 5MB, transferring a mailbox that contains 30MB of content would create six log files just to hold the messages. The IS also expands depending on how much data the mailbox move transfers. Therefore, always ask users to purge their mailboxes before a move. A reduced number of messages makes the transfer of mailboxes proceed faster and decreases the move's strain on the IS.

Users of MAPI clients don't even notice when you use the Move Mailbox function to move their mailboxes. Users of non-MAPI clients (i.e., Web browsers, Post Office Protocol 3—POP3—clients, and Internet Message Access Protocol 4—IMAP4—clients) have to change the server name in their profile to connect to the correct server after you move their mailboxes. But users of MAPI clients don't have to make such a change because Exchange Server redirects MAPI client connections to the new server and updates the profile the first time MAPI users attempt to access their mailboxes after the mailboxes move.

   Previous  [1]  2  3  Next