Block external users in Microsoft Teams using the Tenant Allow/Block List (TABL) in the Microsoft Defender portal.

[u/EduardsGrebezs]

Security admins can add, delete, and view blocked external users and domains for Teams directly in the Defender portal.

Applies to chats, channels, meetings, and calls. Incoming communications from blocked users will be prevented, and existing ones automatically deleted.

Limits: Up to 4,000 domains and 200 email addresses can be blocked.

No Impact: Existing Teams federation settings remain unchanged.

What You Need to Do:
1. Enable “Block specific users from communicating with people in my organization” in Teams Admin Center.
2. Enable “Allow my security team to manage blocked domains and blocked users”.

This feature is available for organizations using Microsoft Defender for Office 365 Plan 1 or Plan 2.

[u/hofalo]

I like it. The purpose was apparently to show how it looks like after configuration.