The Autoconfigure and Autodiscover options in cPanel let you easily configure users' email clients to receive their cPanel emails. This works with email clients such as Outlook Express and Thunderbird.
There are several methods that an email client can try to be auto-configured. Popular methods are Autoconfig (Thunderbird, more*) and Auto Discover (Microsoft, Samsung Android). Autodiscover uses Exchange Active sync (EAS) and Exchange Web Services (EWS) which allows any Email Client that supports Autodiscover to configure the appropriate server settings for communication.
We don't have to enter all the configurations manually. This is very useful for both administrators and users.
Autodiscover also uses SSL certificates. The purpose of auto-configuration is to make it easier for users to configure Thunderbird connections to their mail servers.
And here is an example of configuring a mail client using autoconfig on thunderbird:
