[update 26/09/17] Apple has fixed the problem now with the iOS 11.0.1 update
Do you use Outlook.com or Office 365, or an Exchange Server 2016 running on Windows Server 2016 ?
Don’t update to iOS11 yet !
You may not be able to send email from your updated device and get the message :
“Cannot Send Mail. The message was rejected by the server.”
Stay tuned, Apple is working on it.
At Perfektly, we are fighting toxic and buggy updates with our Tetratine feature. Stay tuned !