Do you know why the error?
(I did try a valid email address instead of what it says in the screenshot)
I believe it is a bug in the Outlook send message action. I can validate the action runs to the point of receiving the data and attempting to actually send.
Can you send from the same account via Mail instead? There should be no difference in what app sends it on to your outgoing mail server.
No i can’t unfortunately send from Mail, because my work email can’t be added to mail accounts… (only via Exchange but then the administrator has control over my device which I don’t want obviously)