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

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.” 


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

Figure 2 – Skype For Business Server lifecycle

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.

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

  • Security: After enabling guest access to external users, IT cannot control or dictate what security measures (such as password complexity, expiration, multi-factor authentication, etc.) external users will use to access their infrastructure. As a result, guest access could be risky for a company’s infrastructure.
  • Cost and Control: Microsoft Teams only allows five (5) free guess access per end-user license. However, there is no limitation or control on how many guest account invites any given users can send out as long as your company stays within its overall limit of the pool. This means IT will only find out when the guest access pool is exhausted when it is too late, and costs start to rise. 
  • Management: When multiple TC platforms are being used internally with guest accounts on each, then IT has to set up and manage different sets of guest accounts using different admin tools.
  • Redundancy: This means the potential proliferation of multiple UC and TC clients on users’ desktop and mobile devices, adding to the learning curve and creating redundancy in communication tools.

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.

Figure 3 – Microsoft Teams and NextPlane’s ConverseCloud

Published 02/24/20