This is connected to a 2009 CVE against common SSL libs ( nss, openssl
etc.) using an insecure form of handshake.
All faulty external mailserver have in common, that they are not
up2date, as they at least do not offer TLS 1.3 encryption.
On was even TLS 1.0 only ..
The question "if OpenSSL 3 is buggy or not" is under investigation atm.
There is a workaround for the issue, but it involves introducing MITM
attackvectors and we don't won't this, don't we? :) (if you need to know
throw me a mail).
