Any good strategy to reform Exchange environment

Since today morning, I am trying to resolve the issue that I feel, its the part of something like Exchange corruption.
I was trying to export some users mailboxes into PST and import them to new server.
After exporting two users mailboxes, I am unable to export remain mailboxes with 0% warning. Though, we do have strong backup policy and now I am planning to extract the data from there.
Your suggestions are highly appreciated !