Cumulative Update 3 for Exchange Server 2016 resolves issues that were found in Exchange Server 2016 since the software was released. This update roll-up is highly recommended for all Exchange Server 2016 customers. You can download Exchange Server 2016 CU3 from here...
Few BIG changes/support/features:

• Windows Server 2016 Support
• .Net 4.6.2 Support
• High Availability Improvements
• Refreshed People Experience in Outlook on the web

For detailed information on new features and supports refer to below articlehttps://blogs.technet.microsoft.com/exchange/2016/09/20/released-september-2016-quarterly-exchange-updates/ Cheers,-Gulab Prasad