If you’re not able to send an email with iOS 11 and Outlook.com or Exchange mail account, then you’re not alone. It looks it is a bug in iOS 11, and Apple is working with Microsoft to fix the issue.
Apple has just published a support article acknowledging the issue:
You might see an error message that says “Cannot Send Mail. The message was rejected by the server.”
If your email account is hosted by Microsoft on Outlook.com or Office 365, or an Exchange Server 2016 running on Windows Server 2016, you might see this error message when you try to send an email with iOS 11: “Cannot Send Mail. The message was rejected by the server.”
Apple says that it is working with Microsoft to resolve the issue but looks like it needs a software update to fix it.
Are you facing the issue? I think the only workaround at this point would be to probably use Safari to login to your account to send an email. We will let you know if there is a better workaround. I am surprised that the issue wasn’t identified during the beta testing process.
We’re tracking all the iOS 11 bugs in this post, so if you’re facing a problem after installing the iOS 11 update then please do let us in the comments section of that post.
Thanks Jason for the tip!