The following instructions will help you to configure brick level backup of mailboxes.
Its recommended to test this instructions on lab before implement them on production
environment:
 
 
1. Give "Receive-As, Send-As" permission to the required user/group by using the Exchange Management Shell command:
 
 
"Get-MailboxDatabase -identity "ServerNameFirst Storage GroupMailbox Database" | Add-ADPermission
 
 -user "DomainNameUserName" -ExtendedRights Receive-As, Send-As"
 
or
 
"Get-MailboxDatabase -identity "ServerNameFirst Storage GroupMailbox Database" | Add-ADPermission
 
 -group "DomainNameGroupName" -ExtendedRights Receive-As, Send-As"
 
 
Note: You may need to need to customize the "Mailbox Database" name so it reflect the real
 
             "Mailbox Database" name .
 
 
How to Allow Mailbox Access
 
http://technet.microsoft.com/en-us/library/aa996343.aspx
 
 
2. To use "Exmerge" utility (Unsupported under Exchange 2007) you need to give
 
             "Exchange View Only Administrator" role to the required user/group by using Exchange 2007 GUI tool or
 
              Exchange Management Shell command:

 
            "Add-ExchangeAdministrator -Identity ‘DomainNameUserName’
 
              -Role ‘ViewOnlyAdmin"
 
Or
 
            "Add-ExchangeAdministrator -Identity ‘DomainNameGroupName’
 
              -Role ‘ViewOnlyAdmin"
 
 
 
Note: Exchange 2007 SP1 32 Bit Management tools + Outlook 2003 SP2 or higher should be installed
 
         on the machine that will be using the "Exmerge" utility.
 
 
3. Verify that the requiring permissions are applied by using the Exchange Management Shell command:
 
      "Get-MailboxPermissions"
 
    Or by using "ADSIEDIT" utility, navigate to: 
 
       “Configuration>Service>Microsoft Exchange>Exchange Org>Admin Groups>Exchange Administrative Group
 
        (FYDIBOHF23SPDLT) >Servers >ServerName>Mailbox Database".
 
       and verify that security settings and "Effective Permissions" are applied.
 
 
4. Use the instructions bellow to export/import mailboxes:
 
 
How to Export and Import mailboxes to PST files in Exchange 2007 SP1
 
http://msexchangeteam.com/archive/2007/04/13/437745.aspx