Error when accessing a domain: HTTP Error 403.503 - Forbidden

Symptoms

• One of the following errors is shown when trying to access example.com domain hosted on a Plesk server:
  

  CONFIG_TEXT: HTTP Error 403.503 - Forbidden
  Detailed Error Information:
  Module IpRestrictionModule

  CONFIG_TEXT: Forbidden
  You don't have permission to access / on this server
  Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request

• Plesk for Linux only: The following error is shown in /var/www/vhosts/system/example.com/error_log:
  

  CONFIG_TEXT: [client 203.0.113.2:59010] AH01797: client denied by server configuration: /var/www/vhosts/example.com/httpdocs/index.php

• Access to the website is denied for all IP's in Deny access to the site section in Domains > example.com > IIS Settings (Windows) or Apache & nginx Settings (Linux)

Cause

Expected behavior according to specified settings - the web server denies access to the domain from all IP addresses.

Resolution

1. Login to Plesk
2. Go to Domains > example.com > IIS Settings (Windows) or Apache & nginx Settings (Linux) and set Default for Deny access to the site
3. Alternatively, add the client's IP address (for example, 203.0.113.2) to the Excluding list