Here is how to turn off junk and spam filtering in Office 365 for all users
You have to use PowerShell, and it takes a specific set of tools and commands that is rather hard to find with all the different variations of Office 365 setups
1) Connect to Exchange Online with MFA Turned On
Make sure that you are using the latest and most up to date version of the Microsoft Exchange Online PowerShell, you can do that by running this command from Windows Powershell which is installed on your computer
Set-ExecutionPolicy RemoteSigned
Install-Module -Name ExchangeOnlineManagement
Connect-ExchangeOnline
2) Disable Spam Filtering for all users with PowerShell
Get-Mailbox | Set-MailboxJunkEmailConfiguration –Enabled $False
or
$All = Get-Mailbox -RecipientTypeDetails UserMailbox -ResultSize Unlimited; $All | foreach {Set-MailboxJunkEmailConfiguration $_.Name -Enabled $false}
3) Disable Spam Filtering for a single user with Exchange PowerShell
If you want to remove spam filtering for just one user enter the command:
Set-MailboxJunkEmailConfiguration user.name -Enabled $false