Introduction
cPanel allows webmail users the ability to reset their email passwords via the login screen if they forgot it. This can be enabled or disabled via the WHM.
Procedure
Via the interface, simply visit "Tweak Settings" and search for "Reset Password for Subaccounts" under the "System" category.
To do so via the command-line, you can use the API.
Enable (default):
whmapi1 set_tweaksetting key=resetpass_sub value=1
Disable:
whmapi1 set_tweaksetting key=resetpass_sub value=0