Skype for Business should use proxy server to sign in instead of trying direct connection

Symptoms

Microsoft Skype for Business 2016 first tries direct connection for the Session Initiation Protocol (SIP) traffic. After it gets time-out, the client will use the proxy server. This causes noticeable delays when you sign in the client.

Resolution

To fix this issue, take both of the following actions:

• Install the update for Skype for Business 2016:

  September 12, 2017, security update (KB4011040) for Skype for Business 2016.

• Create the EnableDetectProxyForAllConnections registry value and set it to 1.
  
  To create the EnableDetectProxyForAllConnections registry value, follow these steps:

  1. Exit the Skype for Business client.
     
     Swipe in from the right edge of the screen, select Search, and then type regedit.exe in the search box. Or, type regedit.exe at the Start screen, and then select regedit in the search results.

  2. Start Registry Editor.

  3. Locate and then select the following registry key: HKEY_CURRENT_USER\Software\Microsoft\UCCPlatform\Lync

  4. On the Edit menu, select New, and then select DWORD Value.

  5. Type EnableDetectProxyForAllConnections.

  6. On the Edit menu, select Modify.

  7. Type 1, and then select OK.

  8. Exit Registry Editor.

  9. Start the Skype for Business client.