Remove MailboxDatabase - This mailbox database contains one or more mailboxes…

A common error, with numerous google search hits to over come the most common problems when deleting a mailbox database. But this is a nasty one, turns out that Set-AdServerSettings -ViewEntireForest $True doesn't always show you exactly what is happening.

This was the case in my case. I couldn't get the database removed, and than i found this.

Delete the mailboxdatabase:
Remove-MailboxDatabase databasename -Verbose

It then shows the reason why it can't be deleted.
In my case it was a systemmailbox that wasnt showing when i did
get-mailbox -database databasename

Now i could see what the reason was why the deletion stopped.

1. Start the Active Directory Users and Computers snap-in.

2. On the View menu, make sure that Advanced Features is selected.

3. Locate the Microsoft Exchange System Objects container.

4. Delete the SystemMailbox{yournumber} item.

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