Knowledge Base

How to blacklist and whitelist domains in Microsoft 365 (Exchange Online).

Anti-Spam Policy 

Use this if you want to block but still allow spam filtering to process messages.

Steps

1. Go to Microsoft 365 Defender

2. Email & collaboration → Policies & rules

3. Threat policies → Anti-spam policies

4. Edit the Default Anti-Spam Policy or create a new one

5. Under Blocked Senders and Domains, add:

   example.com
   

6. Save