[The PHP Mailparse PECL extension is required for parsing email tickets.]

This thread was really helpful, however when I tried to install mailparse (3.1.2) from WHM > Module Installers > PHP PECL (Manage) on our CloudLinux 7.9 instance running cPanel v98.x.x, I got the following error message:

re2c: command not found
...
ERROR: `make' failed

To install re2c on a cPanel system, I found this article published by cPanel:

https://support.cpanel.net/hc/en-us/articles/1500000966161-How-to-install-the-MailParse-PHP-extension

And ran the given commands at the Terminal:

Install the EPEL repository if not already installed.

yum install epel-release

Install the re2c package from EPEL if not already installed.

yum install re2c

Thereafter, I simply went back to WHM > Module Installers > PHP PECL (Manage) and mailparse installed just fine.

I hope this helps!