Apple has released an update to iOS, the operating system for iPhone and iPad that contains a known bug.
The upgrade – iOS 11 – began rolling out on September 19 following Apple’s announcement of the new iPhone 8 and iPhone X smartphones. The bug in this iOS 11 update impacts people who use the built-in Mail app in conjunction with Office365 mailboxes or other Microsoft Exchange servers. Some people with this configuration will not be able to send mail after the upgrade. When attempting to send a new email, the app will fail to send and report the error: "Cannot Send Mail. The message was rejected by the server." In other words, the bug prevents Microsoft accounts from sending emails.
People using the Mail app on iPhone have a few options:
1- Wait until the bug is fixed before installing iOS 11 (your phone will be aggressive about encouraging this install but you can ignore it). You can track the status of the issue on Apple’s Support page.
2- Microsoft advised its email users to download Microsoft Outlook from the app store, which is compatible with iOS 11, to send mail. Outlook for iOS fully supports various email services, including Office 365 and Exchange Server 2016. (Note that some ‘power users’ prefer to integrate Exchange contacts, mail and calendar with built in iOS applications – such as messages, maps, calendar, etc. – and Outlook for iOS won’t allow this integration.)
According to the Telegraph, “While updating the iPhone and iPad operating systems can cause compatibility issues for some apps, this year's problems have been limited compared to iOS 10, which caused ‘bricking’ issues on some iPhones, where some phones are rendered virtually unusable following the update.”
Be aware then many old apps may not work with iOS 11 as the update has left iPhones such as the iPhone 5C and 32 bit apps incompatible. You can check app compatibility in settings. See more about app compatibility in this 9/19/17 Telegraph article: How to check which apps won’t work with iOS 11 before you upgrade.
If you have any questions about the bug in the iOS 11 update, Mail and other app compatibility, contact Sinu for support.