Outlook:
2016,2019,office 365
older Outlook Clients to not respond properly and/or connect properly to cPanel servers due to Outlook 2007, 2011, 2013 relying on TLS 1.0 still.
Outlook 2016 has TLS 1.2 built-in but requires manual enabling as it defaults to TLS 1.0.
Mac mail:
10.4, 10.5, 10.6
Windows mail:
2011, 2012
Thunder bird:
63.0,64.0,65.0,66.0,67.0,68.0