How to block email ID in 0365
In the Microsoft 365 Defender portal
Go to Policies & rules
> Threat Policies > Rules section > Tenant Allow/Block Lists. Or, to go directly to the Tenant Allow/Block List page
On the Tenant Allow/Block List page, verify that the Domains & addresses tab is selected.
On the Domains & addresses tab, click
Block.
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:
Optional note: Enter descriptive text for the entries.
When you're finished, click Add.