I can’t log in into my school account

Dear @Tomáš Pospíchal,

Thank you for reaching out to the Microsoft Q&A Community. 

I understand the issue you're facing. It's certainly a confusing situation when your account works on your PC and iPad but not on your iPhone, especially since you know you're using the correct credentials.

This issue is specific to how the Outlook app on your iPhone is handling the authentication process with your school's custom domain. Since your login works on other devices, the problem is not with your password, but with the app itself or a setting unique to your iPhone.

Here are a few steps you can take to try and fix the problem:

1.Restart the Outlook App and Your Phone:

• Force-quit the Outlook app by swiping up from the bottom of your screen and swiping the app away. Then, reopen it.
• If that doesn't work, restart your iPhone completely.

2.Reinstall the Outlook App:

• This is often the most effective solution for app-specific login issues.
• Delete the Outlook app from your iPhone.
• Go to the App Store and re-download it. This will ensure you have a clean installation without any corrupted cached data from previous login attempts.

3.Try the Web Version:

• Open Safari or another web browser on your iPhone and go to the Outlook web login page.
• Try to log in there. If you can log in successfully on the web, it confirms that the issue is specific to the Outlook mobile app on your iPhone.

If none of the above steps work, the problem is likely related to a server-side setting or a policy that only affects your iPhone. In this case, your best option is to contact your school's IT administrator or help desk.

They can check the security logs for your account and see exactly why the login attempt from your iPhone is being rejected. They can also manually reconfigure your account or check for any conditional access policies that might be blocking your specific device.
For reference: How to troubleshoot sign-in errors - Microsoft Entra ID | Microsoft Learn

I hope this information helps clarify the situation and provides you with workable solutions. Should you have any further questions or need additional assistance, please don't hesitate to reach out. We're always here to help. Have a wonderful day!

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