Most of us as messaging administrators want to delete the default created mailbox database with any new exchange mailbox server

If you tried to delete this default database in normal way you will face the below error

So what to do to delete the default database!!!!!!!

below is the steps needed to delete the default database:

1. Moving Arbitration Mailboxes (System Mailboxes , FederatedEmail) & Discovery mailbox

Get-Mailbox -Arbitration -Database “Mailbox Database 1973945018”
you will get the below result

Now moving this arbitration mailboxes to another DB (MailboxDB) using the below Command
Get-Mailbox -Arbitration -Database “Mailbox Database 1973945018” | New-MoveRequest -TargetDatabase MailboxDB

Now to move the Discovery mailbox , use the Exchange Mangement Console as below

Once all moves are complete, you can remove the move request from the Exchange management console

2. Move Mailboxes exist on this Mailbox Database

you can do that by the following command :
Get-Mailbox -Database “Mailbox Database 1973945018” | New-MoveRequest -TargetDatabase MailboxDB

3. Move any archiving mailboxes exist on this DB

Now get all archiving mailboxes and thier corrosponding DBs
Get-mailbox -archive | fl identity,database

Now move these archiving mailboxes to any other DB
Get-Mailbox -Archive | New-MoveRequest -ArchiveTargetDatabase ‘Mailbox Database’ -ArchiveOnly

4. Now you can delete the default Mailbox Database safely without any problem