The Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities. wikipedia.org

cPanel is a Linux based web hosting control panel that provides a graphical interface and automation tools designed to simplify the process of hosting a web site. wikipedia.org

A message transfer agent or mail transfer agent (MTA) or mail relay is software that transfers electronic mail messages from one computer to another using a client_server application architecture wikipedia.org

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. wikipedia.org

Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks. wikipedia.org

Postfix is a free and open-source mail transfer agent (MTA) that routes and delivers electronic mail. It is intended as a fast, easier-to-administer, and secure alternative to the widely-used Sendmail MTA.

PHP is a general-purpose server-side scripting language originally designed for web development to produce dynamic web pages. wikipedia.org

Red Hat Enterprise Linux (RHEL) is a Linux-based operating system developed by Red Hat and targeted toward the commercial market. Red Hat Enterprise Linux is released in server versions for x86, x86-64, Itanium, PowerPC and IBM System z, and desktop versions for x86 and x86-64. wikipedia.org

MySQL is a relational database management system (RDBMS) that runs as a server providing multi-user access to a number of databases. wikipedia.org