I am working on an Exchange 2010 project (no typo!) where all mailboxes need to be moved to Exchange Online. Since Exchange 2010 is out-of-support for years, creating an Exchange 2010 hybrid environment is not a good idea. So, instead I installed Exchange 2016 and created a hybrid Exchange 2016 environment. But that brings it challenges as well.

The first issue we ran into when creating the hybrid configuration was the TLS 1.2 issue. Exchange 2016 (on Windows 2016) supports TLS 1.2, but it needs to be enabled. To enable TLS 1.2 on Exchange 2016, follow the instructions on the Exchange Server TLS configuration best practices article on the Microsoft website.

When running the Hybrid Configuration Wizard for the first time you must add the domains for federation with Office 365. DNS TXT records were added for all four domains but validating failed after validating the first domain. The wizard hangs on validating subsequent domains.

Removing the other three domains from the wizard and thus validating with only one domain solved our problem and the wizard successfully finished. Later on we were able to add the other domains, but only one at a time.