Hi there, I´m Ivania and I´m glad to help you today.
The Outlook app offers a built-in reset option if emails are not syncing.
Try this:
-Open Outlook.
-Tap on the settings menu and then go to Settings icon.
-Open the Microsoft account that won’t sync.
- Scroll down and tap Reset Account.
If that doesn't work, try remove and add the account again.
perform the same steps as above, instead of resetting the account, you delete it. And add it again.
Try uninstalling and reinstalling the app, or update your Outlook app from the Play Store.
If you've tried restarting the app and restarting the phone, but the Outlook app still doesn't work as it should, you may need to reset the app to fix this issue.
If you use Android:
-Open Settings
-Tap Storage
-Tap Other apps
-Tap Outlook
-Tap Clear Data and Clear Cache button to reset the app.
After completing the steps, the Outlook app will reset to its default settings and you will need to sign in to your email accounts again.
Please let me know if you solved it with these steps.
Best regards,
Ivania