Troubleshoot connectivity issues with the Microsoft Teams client
Most issues discovered with the Microsoft Teams client can be traced back to firewall or proxy connectivity. Verifying that the necessary URLs, IP addresses and ports are opened in your firewall or proxy will minimize unnecessary troubleshooting. For specific information on URLs and IPs required for Microsoft Teams, please see the Office 365 URLs and IP Address support article. The following scenarios require specific URLs and ports to be opened in the firewall.
Microsoft Teams Client Connectivity
Third Party Integration
Skype for Business Interoperability
Skype for Business Client Interoperability