If you have upgraded your device to latest APPLE iOS11 and you are user of O365 for your mail needs you may notice that there is and issue to sync your mail. This is now confirmed by Microsoft and there is work in progress on resolving this issue.
If you are using the native mail app on your iPhone or iPad, and upgrade to iOS 11, you may encounter issues.
How does this affect me?
Due to an incompatibility in the new release of iOS, users of the built-in Apple Mail app in iOS 11 may be unable to sync their Office 365 mailbox or login to their accounts. iOS 9 or 10 users are not affected.
What do I need to do to fix this?
Microsoft and Apple are working to resolve this issue and will post more information to the article, below, when it becomes available. In the meantime, we recommend you download the free Outlook for iOS client, available in the App Store. Alternatively, you can avoid updating to iOS 11 until the issue has been fixed.
No new info has been provided by Microsoft so check and follow up with support in O365.
Refer to Article 4043473