Knowledge Base

Blacklist Emails Office 365

Must have admin privileges and be signed in as admin.

1. In the Microsoft 365 Defender portal at https://security.microsoft.com, go to Policies & rules - Threat Policies - Rules section - Tenant Allow/Block Lists. Or, to go directly to the Tenant Allow/Block List page, use https://security.microsoft.com/tenantAllowBlockList
2. On the Tenant Allow/Block List page, verify that the Domains & addresses tab is selected.
3. On the Domains & addresses tab, click Block
4. In the Block domains & addresses flyout that appears, configure the following settings:
    ◦ Domains & addresses: Enter one email address or domain per line, up to a maximum of 20.
    ◦ Remove block entry after: The default value is 30 days, but you can select from the following values:
        ▪ 1 day
        ▪ 7 days
        ▪ 30 days
        ▪ Never expire
        ▪ Specific date: The maximum value is 90 days from today.
    ◦ Optional note: Enter descriptive text for why you're blocking the email addresses or domains.
5. When you're finished, click Add.