We recommend that you connect your iOS and Android Devices to the Outlook App. Below are alternative options. They are NOT recommended. They must support modern authentication and DUO authentication. They have limited support.
See Switching to the Outlook Mobile App if you have another mail app installed.
NOTE: If you need to remove your account from an app below, follow the steps for your device, but instead of choosing to Add an account, select your account and Remove it. Removing the account will also remove your account from the Calendar, Contacts, and Notes apps if they were added when the account was setup.
NOTE: See also Microsoft 365 Calendaring Issues: Best Practices for Outlook & Mobile Device Users & their Delegates.