An Office 365 SMTP relay not running SSL would be...concerning. And are you sure it does not require any authentication? Because that doesn't seem quite right, either. If the SMTP server requires any of those things and you don't provide them, then you will get a failure.
Working through this SMTP process with my network admin but we keep running into some trouble with smtp.office365.com.
While we continue to troubleshoot, have you had success/problems with smtp.office365.com before?
Do you know any SMTP services that are known compatible such as Mailgun?
So we finally got it resolved and working!
The point of confusion we kept stumbling on is smtp.ssl: true/false field.
Office 365 supports TLS not SSL (so I am told) so we were quite confused when we were making positive progress after this variable was true.
Maybe update the field name to be more wide reaching? Just a thought
"SSL" is basically a generic term for secure connections. Like "xerox" is generic for "copy" even though it's a registered trademark and pedantically wouldn't make sense.