Block a specific external address from attempting to chat in Teams

Dear @DT_2026,

I'm glad that you can find the way to block an external user from attempting to chat in Microsoft Teams. However, at the user level, you can only block an external contact when a chat request appears by selecting Block instead of Accept. However, this only applies to your own account and does not prevent the external user from contacting other people in your organization.

For organization‑wide blocking, an IT admin can block a specific external email address (or an entire domain) in the Microsoft Teams Admin Center or via the Microsoft Defender portal. Once blocked, the external user will no longer be able to send chats, calls, or meeting requests to anyone in the tenant. For reference: Block domains and addresses in Microsoft Teams using the Tenant Allow/Block List

Regarding identifying the external user: if you receive a chat request, the external user’s email address is displayed in the request or chat profile. If no chat request exists, Teams does not provide a way for end users to look up unknown external senders.

If you are seeing unwanted or suspicious messages, I recommend capturing the external email address and sharing it with your IT administrator so it can be blocked tenant‑wide.

Note: Please understand that as a forum moderator, my role is to provide general guidance and troubleshooting support. I don’t have access to internal systems or backend tools, and I appreciate your understanding of these limits.

I hope the information shared helps point you in the right direction. Thank you for your patience and understanding. I'm looking forward for your update.

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Yes. A specific external address can be blocked from attempting to chat in Microsoft Teams, but this is controlled by the organization’s admin, not per‑user settings.

For end users:

• When the external chat request appears, select Block instead of Accept. This stops further Teams communications from that sender to the account.
• Always verify the sender and preview the message before accepting, as external chats can be spam or phishing.

For admins (tenant‑wide blocking of a specific external user or domain):

1. In the Teams admin center, go to Users > External access.
2. To block a specific external user:
   • Turn on Block specific users from communicating with people in my organization.
   • Select Block a user, enter the external user’s email address, and apply. Up to 200 users can be blocked this way.
3. To block all communication from the sender’s domain (if desired):
   • Either configure Block specific domains under Allow or block external domains, or
   • If enabled, let the security team manage blocked domains via the Microsoft Defender portal using the Tenant Allow/Block List on the Teams senders tab, where domains and addresses can be added as block entries.

Once a user or domain is blocked, new Teams chats, meetings, calls, and other communications from that user or domain are prevented, and existing conversations are removed.

References:

• Prevent spam or phishing attempts from external chats in Microsoft Teams
• IT Admins - Manage external meetings and chat with people and organizations using Microsoft identities
• Block domains and addresses in Microsoft Teams using the Tenant Allow/Block List