In a default Exchange 2010 installation when a user account is disabled there is an automatism, in exchange, that delete or disconnect the mailbox associated to the user?
You can either disable a mailbox, which will disconnect the mailbox and leave the AD user enabled, or you can delete a mailbox, which will disconnect the mailbox and disable the AD user. In either case, disconnected mailboxes are cleaned up (removed) after 30 days by default. You can check your actual mailbox retention setting by running:
Get-MailboxDatabase | ft Name, MailboxRetention -a
You can either disable a mailbox, which will disconnect the mailbox and leave the AD user enabled, or you can delete a mailbox, which will disconnect the mailbox and disable the AD user. In either case, disconnected mailboxes are cleaned up (removed) after 30 days by default. You can check your actual mailbox retention setting by running: