Vlad, yes, I saw that mentioned in the 2016 post, but the consultant at the customer replied to us:
"I set it up for port 587 and all works fine. I was able to test it and everything looks good. Port 587, Starttls, No Certificate Verification required."
So, have been going on that assumption.
Is this just a problem with Exchange servers?
Any other time I've needed to connect to a server with TLS/SSL, I've never needed to install a certificate.
We will forward this to their team and see what they can provide.
thx