Teams only - unable to communicate with external Skype for Business users

Copper Contributor

We are using Teams in Coexistence Mode Teams Only (upgraded from S4B). When trying to IM S4B on-premise users we're receiving the following error: We ran into a problem sending your message. Please share diagnostic code 500/16825 with your admin to help them troubleshoot the issue. The user receives the message but is unable to reply. The S4B user's Display Name is shown.


There are no issues communicating with external Teams users.


Microsoft are saying it's a problem on the S4B end but I am able to communicate with these users from another tenant (Teams only).


Does anyone have any ideas what I can check please?


Many thanks




6 Replies



What can you see in the Firewalls in front of your Edge ? Microsoft are correct it's most likely to be something in your SfB environment, typically a firewall only allowing communication in one direction IMHO.

@Steven Collier 


Thanks for the reply Steven. I'm struggling to understand the following:


Source org 1 (Teams only) - destination org 1 (Skype on premise) - only receiving instant messages

Source org 2 (Teams only) - destination org 1 (Skype on premise) - presence working and bidirectional message flow.


Sounds like a configuration issue with Source org 1?

@RichLewis Only if the data is getting there the same for each org, 9 times out of 10 this type of issue is related to a client's firewall not passing traffic as expected, particularly since in your explanation was there was asymmetry happening

@Steven Collier I am getting the same issue from multiple networks (even public ones with now firewall to consider). Doesn't this suggest a configuration issue with source org 1?

@RichLewis It's incredibly unlikely there is an issue with Teams, it's a shared service with millions of customers, you will be getting the same service as anyone else. There isn't anything that you can configure either. Raise a ticket with Microsoft but I am incredibly doubtful there will be issues anywhere other than in SfB On Premises configurations and Firewalls.

Thanks for your input. This issue has now been resolved. The S4B destination had a specific edge server defined in their allowed federation list. Removal of this, leaving just the allowed domain fixed the issue.