Update: Apple has said that upgrading to iOS 11.0.1 or later should resolve this issue.

Apple has reported that those using Office 365 Outlook with the built-in iOS Mail app may get an error stating “Cannot send mail.”  If you’re a faculty/staff member with your BU email on Office 365 Outlook (also known as Exchange), we recommend waiting before updating your phone.  Apple has reported that they are working with Microsoft on a fix.

For those who have already upgraded and are experiencing a problem, you can download the Microsoft Outlook app for iOS.