Mailbox Separation Anxiety

As we have been discussing over the last few weeks, Exchange 2000-2007 runs through quite a few operations during the Online Maintenance (OM) process.  We've talked about how databases get cleaned up, and how messages get deleted (temporarily and then permanently).  This week, let's look at Deleted Mailbox Retention (DMR) and what it can do for you.

DMR is the process that Exchange uses to remove mailboxes that have aged past their expiry date in the Private Database.  These expired mailboxes can be created by different operations within Exchange, either directly by the administrator of Exchange, or by operations in Active Directory that inadvertently cause a mailbox disconnect.  Disconnected mailboxes are simply mailboxes that not longer have an associated user or object in Active Directory. The simplest way to do this is to delete a user account in AD, which will disconnect the mailbox assigned to that user as part of the process.  However, this isn't the only operation that can cause mailboxes to become marked for deletion.  There is an odd side-effect to moving mailboxes that can happen if you jump between AD sites and don't finish fast enough (You can read about it here), and of course; if you get hit with AD corruption it could disconnect mailboxes as well.

Once a mailbox is disconnected, the first OM run that happens after the disconnect will mark the mailbox for expiry in a user-defined number of days. The default is 30 days, so if you run maintenance daily, the mailbox will stay in the database, but disconnected, for 30 days after it is disconnected from the mail-enabled object (like a user) in AD.  It also means you have to take when you do OM into account for your deleted item retention numbers.  For example, if you only do OM once per week, then you will need to add up to 7 days to your overall retention time for planning purposes.  Since the 30 day clock doesn't start ticking until the mailbox is marked during OM, you will extend the amount of time data remains in the database.  This is critical for regulatory compliance, as holding data for an extra week could put you over the line in terms of meeting your regulatory guidelines.

The other part of this OM process happens when Exchange scavenges the database for expired mailboxes.  If it finds one, and the mailbox hasn't been re-assigned to another AD object, Exchange will delete the data from the database permanently and create white-space in the database that gets cleaned up by OM to be reused by Exchange.

So, here again, it becomes vital that OM is permitted to run on a regular basis.  If not, deleted mailboxes will not be removed from the database unless you manually launch the cleanup wizards.  This is more than just a regulatory problem, as without removing the old information and freeing up white space, your databases will grow much more rapidly than if you are regularly cleaning up your mail stores.

Next week... Public Folder operations during Online Maintenance, so stay tuned!