The CreateMailbox procedure enables Exchange mail for an existing user. The subscription record in the Plans database is updated with mailbox information. Mailbox resources are allocated in the Resource Manager database, and mailbox storage is created in the Microsoft Exchange Server 2007 Information Store.

The sequence of steps involved in creating a mailbox for a user is as follows:

1. Allocate mailbox resources in the Resource Manager database.
   
2. Create a mailbox in the Exchange Information Store.
   
3. Add the GUID for the mailbox to the customer record in the Plans database.