Apple started rolling out iOS 11 yesterday. The newest operating system has some great new features, however if you normally use Apple’s stock mail app then you are going to run into some issues with your outlook.com and Office 365 email accounts.
The newest update is blocking Microsoft users from sending emails in the default Apple mail app. According to Microsoft and Apple, users with an Outlook.com, Office 365, or Exchange 2016 on Windows Server 2016 email account may not be able to send emails using the default Mail app in iOS 11. You will get an error message that states: “Cannot Send Mail. The message was rejected by the server.”A fix for the issue isn’t available yet, but Microsoft recommends users to install the Outlook app for iOS as a way to send email until a solution is available.
Both Apple and Microsoft are aware of the issue, and Apple states that they are “working closely with Microsoft to resolve the issue and will release a fix soon in an upcoming software update.”