Microsoft 365 Outlook App. How to enable biometrics or another layer of security on the app

Virtually all phones today have hardware for fingerprint detection or facial recognition. You should enable one of those, so that only you can unlock your phone. This is something you do with the phone, unrelated to Microsoft.

Microsoft 365 apps are a feature of your Microsoft account. Everyone should be protecting their Microsoft account with a passkey, instead of the traditional username and password, so that only you can access your Microsoft account.

From Microsoft: Create and save a passkey

This depend on whether you're using an iPhone or Android.

If you're using an iPhone

On iOS 18 or later: Locate the Outlook app on your Home Screen> Press and hold the Outlook icon> Select Require Face ID (or Touch ID).

Or in the Outlook app Settings > Toggle on the FaceID option.

If you're using Android

I don't think Outlook has a general, user-configurable biometric app lock for personal accounts on Android.

If this is a work or school Microsoft 365 account

Your IT administrator can use Microsoft Intune app protection policies to require a PIN or biometric authentication before users can access their work emails.