Basic Authentication Deprecation in Exchange Online – September 2022 Update

zach_johnson : For Apple devices, make sure they are iOS 11/macOS 10.14 or later (https://support.apple.com/guide/deployment/integrate-with-microsoft-exchange-dep158966b23/web#:~:text=Modern%20Authentication%20support%20for%20Exchange%20accounts). When adding the account to the Mail app, select "Sign in", not "Configure manually" after entering the email address/account description and tapping Next. This should open the modern auth webview to sign in. Some more information specific to Apple devices is in a previous blog post here: https://techcommunity.microsoft.com/t5/exchange-team-blog/microsoft-and-apple-working-together-to-improve-exchange-online/ba-p/3513846 

For Android devices, if they're using the Gmail app, delete the account and add it again. Don't tap the manual configuration option, and it should display the modern auth (Microsoft sign-in webview) after you typed the email address. In Samusung Mail, delete the account and add it with the Office 365 account type (not "Corporate" or "Exchange server").