Apple has released a fix (update 11.0.1 or later) for users not able to send email with native email client connected to an Office 365 or Exchange account:
On Tuesday, September 19, Microsoft released a notification of a known iOS 11 compatibility issue with Office 365 mailboxes. Individuals with Iphones or Ipads utilizing the built-in Apple Mail app with iOS 11 may be unable to sync their Office 365 mailbox. IPhones or Ipads that are running iOS 9 or iOS 10 do not appear to be affected.
Microsoft has stated they are working with Apple to resolve this issue. At this time we do not have an estimated time of resolution from Microsoft or Apple.
UCF IT recommends that any individual that is currently using the native Apple Mail app to access their UCF Office 365 mailbox not upgrade their device to iOS 11 if they wish to continue using that application for email. As of this writing, Microsoft recommends that any individual using iOS 11 use the Outlook for iOS email client or other third party to access email because of this documented incompatibility.
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