Microsoft Lync/Skype for Business users were not able to connect to lync server over Internet

Check the following

Check internal SSL Certificate Expiration date installed on Lync Edge server

Check External SSL Certificate expiration date installed on Lync Edge server

How to Check the above:

• Open “Lync server deployment wizard” in Lync edge server from start menu
• Click Intall or Update Lync server system
• Click RUN Again under Request,Install or Assign certificates
• Certificate wizard will open

Resolution:

• If any internal SSL certificate is expired then generate certificate from your internal Certificate authority server.
• If external SSL certificate is expired the generate the certificate from external certificate authority like Digicert/Godaddy etc..
• Go to Lync server deployment wizard & under certificates click import
• Then click assign and select the certificate & click finish.
• Go to services.msc & start the lync services
• Now check the users login status