Today I discovered that you can completely turn off the Junk Mail folder for an Exchange Online/Office 365 mailbox!

To do this, you’ll need to run the following from an Administrative power shell window:

Set-ExecutionPolicy RemoteSigned
$Cred = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $Cred -Authentication Basic -AllowRedirection

Import-PSSession $Session

Set-MailboxJunkEmailConfiguration "Firstname Surname" -Enabled $false