All customizable web server settings are located in Websites &
Domains > select a website > IIS Settings. Custom settings work
only for the selected website.

The settings are divided into groups:

Common Settings

These settings are typically changed by site owners, who may want to:

• Allow site visitors to view the listing of files and subdirectories
  of the site’s directory in their browsers (Directory browsing).
  The directory listing will be displayed if there are no matches for
  default index pages in the site’s root directory.
• Add a type of default index pages (Default documents).
• Add a MIME type for files with a certain extension (MIME types).

Directory Security Settings

These settings allow site owners to:

• Restrict access to the site by username and password – only system
  users will be able to access the site (Anonymous access). Denying
  anonymous access may be useful if your site is not intended for any
  visitor, for example, it is a web application for external use. Note
  that FTP users and additional FTP users created in Plesk will have
  access to such a site if they were granted access to the site’s
  directory.
• Force all clients (such as browsers or FTP clients) to use the secure
  HTTPS protocol to access their site (Require SSL/TLS). You need
  this option, for example, if the site contains and transmits personal
  information.

Access Restriction Settings

These settings allow site owners to restrict access to the site by IP
address of the visitor (Deny access to the site) by denying and
allowing access from certain IP addresses.

If you do not find the necessary setting, contact your server
administrator (hosting provider), who can set up more custom settings
for websites.

The Default Value of Server Settings

You can set the value of each parameter either by typing a custom value,
or leaving the Default value. In the latter case, Plesk uses the
values from the default web server configuration defined by the server
administrator (hosting provider).

Your values override the default ones. The only exception is the Deny
access to the site setting - IP addresses from the default
configuration, as well as the IP addresses specified by you, will all be
applied to your website. In case of a conflict (for example, when you
allow the IP address that is denied in the default configuration), IIS
uses your settings.