Using Outlook for Android in business environments for email and scheduling
Thanks for pointing me in this direction :-) I too had a problem with SMTP protocol settings. Having admin-control over my SMTP-server (Postfix) I managed to dig into the server-logging to see what was actually happening during the connection-attempt.
The server was configured as STARTTLS on port 465. The Outlook client does not do STARTTLS, as shown by the server log: first the client connected (at port 465) and then immediately disconnected without issuing the STARTTLS command.
Solution was to change the server-config for port 465 by making it "pure TLS" instead of STARTTLS. Each new connection is immediately thrown into TLS encryption by the server without waiting for the STARTTLS command.