Recently we have enabled SSL Inspection in our organization and today I got a lot of complains about not working Skype for Business meetings with external companies not using Office 365. I have troubleshoot and it seems the Skype for Business client can’t correctly use the Zscaler Intermediate SSL certificate within the connection. I have added the addresses of the external companies Skype instances to the SSL Inspection exception list and now it works. I have seen the option to except certain applications from SSL Inspection and have activated the category Collaboration and Online Meetings and Commone Office 365 applications but both not matching connection from Skype for Business client. It is possible to add Skype as an application to the available application exception inside SSL Inspection (Policy => SSL Inspection => Do Not Inspect these Applications).