Michel de Rooij did a nice article on how to configure Thunderbird for oAuth2 which you can read here: Configuring Exchange Online with IMAP & OAuth2 In order to leverage this functionality mail clients need to start using it (so they need an update). Update: On April 30 2020, the Exchange Team announced that OAuth 2.0 authentication for IMAP and SMTP AUTH protocols is now available. Update: On April 3rd 2020, the Exchange Team announced that due to the COVID019 crisis, they will postpone disabling legacy authentication until the second half of 2021. They also announced that they will add support for Modern Authentication into the MAPI, RPC, and Offline Address Book (OAB) protocols. They did announce that they will continue to turn off Basic Authentication protocols not in use within tenants. When they resume the program, they will let customers know with a 12 months notice. Update: On February 5th, 2021, the Exchange Team announced that turning off legacy authentication in H2, 2021 is postponed until further notice. Update: On June 17, 2021, the Exchange Team announced that they are going to turn of basic authentication for tenants not using it. Update: On September 23, 2021, the Exchange Team announced that effective October 1st, 2022 basic authentication, regardless of usage will be permanently disabled in all tenants.

Office 2013 modern authentication