Microsoft Teams to Skype for Business Server Federation is Going Away Soon

Nextplane Inc.
3 min readFeb 24, 2020

On 30/07/2019, Microsoft announced retiring Skype For Business (S4B) Online. As a result, all Skype for Business Online customers will be on Microsoft Teams before July 2021. Today, organizations on Microsoft Teams can federate with users on Skype for Business Server using the SIP Interoperability Gateway of Skype for Business Online. This feature is called External Access in Microsoft Teams. Through External Access Teams, Teams users can chat and make audio/video calls in a one-to-one scenario. You can find a detailed list of available features on

Figure 1 — Microsoft Teams to Skype Onprem federation over the interoperability gateway

Since Microsoft is also retiring the SIP interoperability gateway of Skype for Business Online, customers on Microsoft Teams can not communicate with their external partners on S4B Server. Even today, this kind of federation is not available already for some customers as it requires a Hybrid Skype setup:

“Currently, to federate within the Microsoft Teams app to an external user outside of your organization who’s not currently a guest of your Azure Active Directory (Azure AD) or tenant, you must be correctly set up for hybrid and moved to Skype for Business Online. As of February 25, 2019, Teams doesn’t support native federation without the user of the SIP profile being homed in Skype for Business Online.” Source:

Figure 2 — Skype For Business Server lifecycle

This is going to be a problem as Microsoft plans to support customers on Skype for Business Server (S4B) 2015 or 2019 until 2025.

To get around the problem of interoperability between MS Teams and S4B Servers, Microsoft is recommending MS Teams customers to use the Guest Access to communicate with their external partners.

Figure 3 — Microsoft Teams and NextPlane’s ConverseCloud

However, this approach overlooks the following limitations of using MS Teams Guest Access.

For a more in-depth analysis of MS Teams Guest Access, please visit our Common Pitfalls of MS Teams Guest Access Blog.

Based on our market research, IT leaders need a seamless solution to connect organizations on MS Teams and to ones on S4B Servers. They need a universal hub that performs the necessary SIP protocol translations and API conversions to ensure all messages, presence, group participation in Teams flows seamlessly, and file shared regardless of platform.

Furthermore, our research shows that most IT organizations do not want Guest Access holders to have permanent access to their environment. NextPlane offers an API based solution so Microsoft Teams users can search and add S4B contacts, share presence and status, exchange messages, participate in Teams, send rich text and emojis, and share files with their colleagues.

Originally published at on February 24, 2020.