Apple Mail: Only TLS v1.0 supported on macOS 10.11 I'm on OS X 10.11.3, aka El Capitan.

I can't connect to mail servers running only TLS version 1.2 or 1.1 with Apple Mail.

IMAP as well as SMTP connections are always established using TLS 1.0.

Could that be correct?

If so, why doesn't Apple Mail support TLS 1.2 yet?
This seems to be an issue with MacOS El Capitan and lower versions.  Upgrades to Sierra and High Sierra resolve the issue.  

However, there needs to be a solution for users on computers which cannot upgrade to Sierra and higher.