The employee forgot to put out of office reply in Outlook before you leave on vacation. Is there a way for an administrator to do it for the user without knowing his password? running Exchange 2007
The following steps that you need.
To get started in the shell, go to:
Start > All Programs > Microsoft Exchange Server 2007 > Exchange Management Shell
This opens a window that looks a lot like a normal command window but, instead of using the old cmd.exe in the background, this is the new, rather plain-looking PowerShell.
Run the command from exchange shell:
Add-MailboxPermission -[mailbox name] -User [Your admin account] -AccessRights FullAccess.
From that point, you have full control of the mailbox and should be able to access it with your credentials.
I hope this helps. Please, let me know if you're still getting hung up.
P.S. Look this issue here. Maybe it will be useful to you.