If users upgrade to iOS 12 within the next hours, they may face a problem. There is a known bug in Exchange Active Sync support that occurs under iOS 12 in the native mail app (but not in the Outlook app).
I became aware of this problem yesterday via Twitter. Tero Alhonen points out that the iOS 12 email feature causes a problem with Exchange Active Sync (EAS) in conjunction with Intune and the iOS 12 mail app.
There’s a known issue with iOS 12 native email, Exchange Active Sync, and Intune for Office 365 Conditional Access Policies https://t.co/sdpToSfTGY … request your end users hold off until September 19th before updating to the latest version of iOS… pic.twitter.com/AFizPa40FK
— Tero Alhonen (@teroalhonen) 17. September 2018
Microsoft has published this Technet blog post with more details about that issue. Microsoft confirms the known issues with iOS 12, in combination with EAS and Conditional Access Policies. Microsoft is working on a fix and plans to release it as soon as possible, max. 48 hours after iOS 12 has been available.