When you set a proxy auto-configuration (PAC) script file in Microsoft Lync Online client, the following issues occur:
You cannot sign in Microsoft Lync Online server.
Sometimes, you cannot search contacts in Microsoft Lync 2013 (Microsoft Skype for Business).
This issue occurs because Lync 2013 (Skype for Business) sets incorrect proxy settings for the Microsoft Online Sign-in component.
To fix this issue, follow these steps:
Install the December 8, 2015 security update (KB3114351) for Lync 2013 (Skype for Business).
Set the value of the HttpProxyControlFlags GPO to 3.
Note Lync 2013 was upgraded to Skype for Business in April 2015.
To work around this issue, use a named proxy server in the Internet Explorer LAN setting instead of setting a PAC script file.
After you apply this update, the HttpProxyControlFlags Group Policy Object (GPO) is added to control proxy settings.
Note The new HttpProxyControlFlags GPO are located in the following registry subkeys:
The default value of the new HttpProxyControlFlags GPO is 0. This instructs the Lync 2013 (Skype for Business) client to set proxy settings for the Microsoft Online Services Sign-In Assistant (MOS SIA) component.
A value of 3 indicates that the MOS SIA component controls the proxy settings by itself.
For more information about the new HttpProxyControlFlags GPO, see An introduction for the new HttpProxyControlFlags GPO in registry key.