cPanel & WHM version 11.52 will no longer support migration from Dovecot to Courier.
Users who are running Courier can continue using Courier for the life of 11.52 however all support for Courier will end in 11.54. Servers using Courier will automatically convert to Dovecot when they update to cPanel & WHM version 11.54.
New installs of cPanel & WHM will not offer the ability to install or use Courier as the Mailserver, and we removed the Courier option from the Getting Started Wizard.
We made this decision because Dovecot has proven to be a much more reliable and more commonly used Mailserver. Please read our documentation for more information on Dovecot.