When you create a new Mailbox, you may get the following error:
Error: Load Balancing failed to find a valid Mailbox Database
as shown below:
When you create a new mailbox, you must select the database.
To fix this, run the following:
PS > Get-MailboxDatabase | Set-MailboxDatabase -isexcludedfromprovisioning $false
The IsExcludedFromProvisioning parameter has have two valid values, $True and $False. When you set this property to $True, the mailbox database is excluded from the automatic distribution process. When you set it to $False, the mailbox database is included in the automatic distribution process. The default value is $False.
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