Removing the first Exchange 2010 database requirements

Run this command first
Set-AdServerSettings -ViewEntireForest $True
The first thing you must do is move all the mailboxes to another database. This can be accomplished via this command
get-mailbox –database “Database You’re trying to remove” | new-MoveRequest –targetdatabase “Database to move users to”
Now you must move the arbitration mailbox
get-mailbox –arbitration –database “Database You’re trying to remove” | new-MoveRequest –targetdatabase “Database to move users to”
You can now check the status of the mailbox move
get-moverequest
Once they are all completed run this command to remove the request
get-moverequest | remove-moverequest
You can now remove your mailbox
Remove-mailboxdatabase –id “Database You’re trying to remove”