Microsoft are going to disable Basic Authentication at the beginning of October 2022, once this happens your tenant will be unable to access their Exchange Online mailbox using Basic Authentication. Microsoft added this feature to help minimize disruptions as you transition away from using Basic Auth. If you receive a Message Centre post between now and Oct 2022, informing you that Microsoft is going to disable Basic Auth for a protocol due to non-usage, or you get one saying they know you are using Basic Auth, but they intend to proactively disable it for a short period of time, and you don’t want us to disable specific protocols, you can use the new self-service feature in the Microsoft 365 admin centre to opt-out and request that they leave specific protocols enabled until October 2022. From October 1st 2021, Microsoft will begin to disable Basic Auth in all tenants, regardless of usage. Microsoft have announced that they are restarting their program to end the use of Basic Auth in Exchange Online.

Exchange multi factor authentication