If your Office 365 email works in the built-in Mail app on iPhone or iPad but encounters issues in the Outlook mobile app, the problem may stem from app-specific compatibility, account configuration, or device-level settings.

🧭 Key Points:

• The Mail app uses native iOS protocols (like Exchange ActiveSync), which may handle certain configurations more smoothly.
• The Outlook mobile app relies on Microsoft’s cloud-based authentication and may require additional permissions or updated credentials.
• If your email account is provided by IIJ (Internet Initiative Japan), it may have unique configurations that behave differently across apps.

🔧 Suggested Troubleshooting Steps:

1. Reinstall the Outlook App
   • Delete and reinstall the app to ensure a clean configuration.
2. Try the Built-in Mail App
   • If the Mail app works without issue, you may continue using it as a stable alternative.
3. Confirm Account Type and Settings
   • Check whether your account is set up as Exchange, IMAP, or POP—this affects compatibility.
4. Escalate if Needed
   • If the issue persists only in Outlook, your IT team may need to escalate to Microsoft for deeper investigation.