We want to migrate our Exchange servers to a new environment and get off some storage that's about to have its support expire, we are currently in a hybrid (On-Prem - O365) environment, so we have moved 95% of our mailboxes to the cloud already.
Regarding freeing up whitespace, I think the easiest thing to do is create a new mailbox database and move the remaining mailboxes to it, instead of taking it offline and defragging, correct?
How can I find out how large the new mailbox database 'should' be? Is it just a matter of exporting a list of all on-prem mailboxes and their sizes and base the new database sizing on that total?
Thanks in advance.