Exchange 2003 – System Mailboxes

A customer recently advised that they were having issues with their archiving product due to the System mailboxes being AWOL. Not being aware of their purpose, how they are created or what they contained, I  looked further into System Mailboxes. This is a summary of what I found.

What is it?

The System Mailboxes are in the format ‘SystemMailbox{guid}’. The GUID is the “objectGUID” of the mailbox store with which the System Mailbox object is associated.

System Mailboxes contains a ‘schema-root’ top-level folder which provides the structure for defining the schema.

The ‘Top of information folder’ contains a ‘StoreEvents’ hierarchy which holds the event sinks attached to this mailbox store.

So basically the System Mailbox contains the schema and information for event sinks, such as the Auto Accept Agent, the Quota Message Service, or third-party event sinks.

Where is it?

The mailbox object is located in the associated mailbox store. The mailbox also has an associated directory object which is located in the Microsoft Exchange System Objects folder in AD, along with all the other public folder and system directory objects.

How is it created?

When the mailbox store is mounted, the mount process checks for a SystemMailbox{guid} mailbox object. If it can’t find one, it looks in AD for the SystemMailbox{guid} directory object, and uses this to create the SystemMailbox{guid} mailbox object within the mailbox store.

How do I recreate it?

So, back to the problem at hand. The customer has no mailbox object or directory object for the System Mailbox, so how do you recreate them?

The Microsoft article KB316622 recommends creating a new mailbox store on the server, moving all mailboxes onto this new store and deleting the old (system mailbox-less) store.

Failing this, the user account can be manually created using ADSIEdit. A full step-by-step is given in the KB article above.

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