V-79-57344-764 - Unable to restore any content for alias because the Microsoft Exchange database that hosts that mailbox is offline or the mailbox doesn't exist.

Thank you all for the support. I finally resolved the issue. Issue was with name resolving. Display name had a special character "," in it and alias wasn't resolving to it. I created a dummy mailbox with first alone so than alias and display name would be same. Redirected restore to that worked fine. also, backs were from 2010 R1 and i upgraded it to 2010 R3 last week. All restore from backups of 2010 R3 looks good.