Enterprises using Office 365 will want to hold off upgrading iPhones and iPads to the latest, greatest operating system version, as the Mail app on iOS 11 is incompatible with Office 365, as well as Exchange Server 2016 and Outlook.com.

More specifically, you can't send or reply to messages, according to an article on the Microsoft Corp. (Nasdaq: MSFT) support site.

Microsoft suggests downloading the free Outlook for iOS client from the iOS App store. Also, "If you use the Mail app to sync data from Exchange Server 2016 that is running on Windows Server 2016, you can ask the system administrator to disable HTTP/2 in Windows Server 2016 as a workaround. The instructions on disabling HTTP/2 can be found in the Workaround section of KB 4032720: How to deploy custom cipher suite ordering in Windows Server 2016," Microsoft says.

Figure 1: Man purchases iPhone at Regent St., London. He'll be less happy if he goes back to work and tries to get his Office 365 email. Photo from Apple.

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Microsoft and Apple Inc. (Nasdaq: AAPL) are working on a fix, and will post more information to the support article when it becomes available, Microsoft says.

Apple says on its support site that users experiencing the problem will see the error message "Cannot Send Mail. The message was rejected by the server." The two companies are working on a fix, and will resolve the problem in an upcoming software update, Apple says.

The bug persists despite users reporting this problem in the iOS 11 beta as far back as July.

"This really pisses me off," says a person on Reddit. "Apple has known about this ever since beta 4 or 5 and have done nothing about it. This is a big bug and lots of people use exchange servers."

The Register is having fun with this one. Attention adults working in the real world: Do not upgrade to iOS 11 if you use Outlook, Exchange. The article refers to Apple as the "Cupertino idiot-tax operation."

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— Mitch Wagner Editor, Enterprise Cloud News