Update: I am still able to send and receive emails with Outlook 5.0 on Windows 3.11 guest VM, using stunnel on host machine.
I am looking for a way to make stunnel work with office365, I've recovered my old first Hotmail account but so far I can only receive, not send. I need to figure out why it is not sending. For Outlook 6.0+, stunnel is not required, because Windows 3.11 mail/web programs (IE5.01, OE 5.0) can only go up to SSL 3.0.
But seeing how roytam1 went as far as giving TLS 1.2 support to older Firefox for Windows 9x+, I tend to think why it would be difficult to do the same for any 16bit software... like... Netscape, the direct grandfather of Firefox?
EDIT: Seems that the problem with the SMTP on office365 (smtp.office365.com:587) has to do with the authentication. I can connect to the server, but I can not authenticate. Strange. I can retrieve my emails with pop3 though...
EDIT 2: It's definitely an authentication problem. Gmail accepts plain authentication when less secure apps is ON, but office365 does not have a such setting to "unlock" this.
EDIT 3: And office365 will never have it. Seems that since 2017 it has disabled plain authentication for it. I can receive emails, but not send. I still believe that it would send emails if I had the right PEM certificate for it. (Has to be DigiCert Cloud Services certificate). We will never know.
Anyway seems that I will be forced to stay on Gmail for legacy email services while I use a 2nd account for that with Less Secure Apps enabled. It's a safe decision.
"Design isn't just what it looks like and feels like. Design is how it works."