This knowledge base document shows how to allow or block specific external senders or domains from contacting users within your organization. Applying this block ensures the specified sender or domain is completely restricted from reaching anyone in Roundel organization.
- Within Microsoft Defender (security admin center) scroll down to 'Email & collaboration' and click Policies & rules
2.When on the Policies & rules page click on 'Threat policies' and then under rules 'Tenant Allow/Block Lists'
3. When on the Tenant Allow/Block page click 'Block' and input the domain or address afterwards set the 'Remove block entry after' to never expire and click add
