For instance imagine that you have a disabled mailbox in Exchange server 2010 which you need to be reconnected back for some reason. Now you are reconnecting the mailbox to its user objects using the Exchange management console.

Now here is the problem! You will see the mailbox as disabled if you check it from the Outlook Web Access although on the Active directory user object will show as this email already mapped.

It will take another 24 hours to take to this mailbox to become active. The reason is a scheduled mailbox clean-up will happen every night on all your exchange server databases. But in most of the cases as per the business requirement you will have to provide the mailbox asap.

You can apply mailbox clean-up command on the server with Mailbox role to enable a reconnected mailbox.

Get-MailboxDatabase | Clean-MailboxDatabase

(This command will clean up the entire databases on that particular server)

If your exchange environment is really large and huge databases its recommended that you clean only that specific database. To clean specific database perform the below command.

Clean-MailboxDatabase database name