Plesk manages the work of web, mail, DNS, and other services. Technically, Plesk does not provide the services by itself; it just takes control over a number of third-party components. For example, when a customer creates a website through the Plesk GUI, Plesk propagates this request to a web server (Apache or IIS) and the latter adds a new virtual host to the system. The list of components is defined during Plesk installation (see the Deployment Guide for details). Plesk allows you to view the list of installed components, add new ones, switch between interchangeable components, and remove them (only in Windows).
You can view the list of installed components and their versions in Tools & Settings > Server Components. Plesk for Windows has an additional indication of a component state (the appearance of the icons depends on the Plesk theme):
If you did not include a component in your Plesk installation, you can add it later in Tools & Settings > Updates and Upgrades > Add Components.
Some Plesk components are interchangeable. For example, in Windows you can use either MS DNS Server or BIND as your DNS server; in Linux you can choose between Postfix and Qmail for mail delivery, and so on.
On Plesk for Linux, you can switch between interchangeable components in two ways:
On Plesk for Windows, you can switch between interchangeable components in Tools & Settings > Server Components. To perform the switch, click on the component name (for example, Mail Server) and select the required component from the list.
If you no longer need a certain Plesk component, you can remove it from Plesk in Tools & Settings > Updates and Upgrades > Add/Remove Components or by clicking the Add or Remove Components link on the Home page.