MS 365 Whitelist a Domain using Security Center, Windows Defender
1- Click on Policies & rules
2- Select Threat Policies
3- Open Anti-Spam (it can take a couple of seconds to load the policies)
4- Click on the Anti-spam inbound policy (Default)5- Scroll all the way down in the fly-out and click on Edit allowed and blocked senders and domains6- Click on Allow domains
7- Add the domains that you want to whitelist
8- Click Done and Save
Mails sent from this domain should now arrive in the inbox and completely bypass the spam filter. But keep in mind, when you whitelist a domain this way, that spoofed email won’t be noticed as well.