How to automatically configure email (Thunderbird, Outlook, and iOS/OSX Mail) with Nethserver

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From Internal (green) Netwerk, it reports an Certificate Error reporting the DNS of Nethservers FQDN as invalid. I suppose it expects an Certificate for autoconfig.myname.tld instead of nethservername.myname.tld. I am wondering at as as no virtual host vor autoconfig.myname.tld is set up. However, I did not manage to fullfill all steps of installation procedure for iphone. Additionally, I am wondering, why I use option [2] - webroot - instead of autoconfig. Or is this because webroot meens any DNS not explicetly defined -> autoconfig.myname.tld = webroot as long no vhost ist defined?

From External source, no error is reported, it does simply not work. I leads me to manual configuration.

TIA
Thorsten