Earlier quoted context omitted.
Indeed it appears to be a long running broader bug [1] of 7 years . Perhaps someone could increase log and header verbosity or enable some form of debugging to see what behavior WhatsApp is invoking. It appears this [2] is how to enable debugging in OpenSMTPD. Once enabled one could trigger an email through WhatsApp to see specifically what it doing. I am nosy and curious enough that I hope someone posts the debug ou…
I'll see your 7 and raise you 10. * https://github.com/OpenSMTPD/OpenSMTPD/issues/451
And more evidence to add to the server-does-negotiated-SSL-but-client-is-doing-implicit-SSL pile is this:
* https://marc.info/?l=opensmtpd-misc&m=141543622103232&w=2
Coincidentally, I was just talking about the mess that SMTP got into with all this.