We can't set up the conversation because your organizations are not set up to talk to each other.

KevinTParker 

Hi,

I'm not sure if this is helpful to anybody who's still having this issue around. Since last week I have been receiving complaints about this exact issue from one of our clients and I don't see many articles on the internet, let alone a concrete solution for this issue. Below given is the issue screenshot our client have sent us.

Actual Issue

Anyhow, I was just having a look at our client's tenant configuration using PowerShell because going to https://admin.teams.microsoft.com/ > Org Wide Settings > External Access / Guest Access doesn't help at all.

I came across this interesting finding:

Verifying Tenant Federation Settings

Why the above finding was interesting, because both on the Teams Admin Center and SfB Legacy Portal we did not block or allow any domains at all. It's open federation, therefore we should not have any domains listed under AllowedDomains parameter above.

I had to go to Skype for Business Legacy Admin portal > Organization > External Communications > External Access = On except for blocked domains. Give it some 10-15 mins, you will be able to chat and view free/busy info with External Users now.

After I made this change, ran the same command to verify the federation settings. This is how it has changed now.

Stay Home, Stay Safe. Utilize lockdown days for your family 🙂

Thanks,

Naveen