Adding allowed senders and domains in the anti-spam policies should be avoided.
You have a number of choices as documented here to allow these messages:
create-safe-sender-lists-in-office-365
I would also recommend running the Best Practices tool against your Office 365 policies and fixing any issues as you deem fit:
recommended-settings-for-eop-and-office365-atp
There is a new PowerShell Module that you can download called the Office 365 Advanced Threat Protection Recommended Configuration Analyzer (ORCA) that helps determine some of these settings. When run as an admin in your tenant, Get-ORCAReport will help generate an assessment of the anti-spam, anti-phish, and other message hygiene settings. You can download this module at https://www.powershellgallery.com/packages/ORCA/.