Hi,
we recently switched email services and at the moment I try to get bugreports using smtp.office365.com (port: 587, TLS). As it seems connection is established and there is TLSv1.2 communication with the server (used Wireshark to sniff packages). At some point I see stuff like:
Using Wireshark is what I'd do myself to debug this, plus maybe set breakpoints in madExcept.pas to figure out at which code location it fails exactly.
I don't have an office365.com email address, so I can't really test it. Could be a bug in madExcept, or maybe Microsoft's TLS implementation (which madExcept is using) might be broken or incomplete. It's hard to say for me.
Maybe you could give debugging a quick try? You can do that by copying madExcept.pas and mad.inc into your project folder. Afterwards you should be able to set breakpoints in madExcept. SMTP mailing is done by calling "TSmtp.Create", then the methods "SendMail" and "Finalize".