Microsoft Exchange 2010: Steps to restore deleted mailboxes of an organization

 
If someone mistakenly deletes an organization, then all mailboxes of this organization are disabled by HC and sent to 'Disconnected Mailboxes" in EMC. 
Following method can be used to restore these mailboxes into Exchange and HC. 

1. Identify mailboxes 
   If domain name is "abc.com" then you have to run following command in shell to get all disconnected mailboxes of this    
   domain, created by HC.
   Get-mailboxDatabase |Get-MailboxStatistics |where {$_.disconnectDate -ne $null -and $_.LegacyDN -like '*_abc.com'}|fl
   displayName,LegacyDN
 
This command would list all disabled mailboxes of a single domain, which you have to enable. Your organization might have more than one mail domain, so you have to run this step for each of the mail domain.
 
2. For each disabled mailbox, either use an existing AD user or create a new user and Restore mailbox using EMC. Either, client would provide password, or  assign any password to newly created users

3. Add user to HC organization security group (org_DL) using ADUC console.
4. Enable disabled Mailbox using EMC, and modify its primary email address in EMC.
5. Set HC attributes on mailbox: 
   a. For Exchange 2010 RTM and earlier versions, set customAttribute2, offlineAddressBook, msExchQueryBaseDN
   b. For Exchange 2010 SP1 and later with HC build 13 , set customAttribute2, offlineAddressBook
   c. For Exchange 2010 SP2 and later with HC version 9 , set customAttribute2, and AddressBookPolicy