MS Teams – “We can’t set up the conversation because your organizations are not set up to talk to each other”

If you try and make contact with someone outside your organisation within Teams you may find that when you search for them you receive the message: “We can’t set up the conversation because your organizations are not set up to talk to each other.”

The reason for this is usually your 365 tenant, or the person you are trying to reach, has the External Access set to ‘Block external domains’ within the Teams Admin centre. The setting of Block All was the default, but (allegedly) the default for newer tenants has changed to ‘Allow All’. Irrespective, if you want to change the setting to allow communication with select external domains (note that they must also allow you to communicate with them of course), you can make the change as below:

To allow specific domains

1. In the Teams admin center, go to Users > External access.
2. Under Choose which domains your users have access to, choose Allow only specific external domains.
3. Select Allow domains.
4. In the Domain box, type the domain that you want to allow and then click Done.
5. If you want to allow another domain, click Add a domain.
6. Click Save.

To block specific domains

1. In the Teams admin center, go to Users > External access.
2. Under Choose which domains your users have access to, choose Block only specific external domains.
3. Select Block domains.
4. In the Domain box, type the domain that you want to allow and then click Done.
5. If you want to block another domain, click Add a domain.
6. Click Save.

NOTE: You can specify which domains are allowed or which domains are blocked. If you specify blocked domains, all other domains are allowed; if you specify allowed domains, all other domains are blocked.

For more detail, PowerShell commands, and how to block subdomains, review the Microsoft KB article.