Webmail on Plesk server is not available: 404 Not Found/403 permission denied

Symptoms

• Unable to open the Webmail going to Domains > example.com > Email Addresses > Webmail, it might show one of the following error messages:

  Not Found
  The requested URL /roundcube/index.php was not found on this server.
  Apache Server at webmail.example.com Port 80

  404 - File or directory not found.
  The resource you are looking for might have been removed, had its name changed, or is temporarily unavailable.

  HTTP 404. The resource you are looking for (or one of its
  dependencies) could have been removed, had its name changed, or is
  temporarily unavailable. Please review the following URL and make sure
  that it is spelled correctly.
  Requested URL: /default.aspx

  Plesk default page

• Going to Domains > example.com > Web Hosting Access > The IP address assigned to the domain example.com in Plesk is 203.0.113.3

Cause

The DNS record for the webmail DNS record webmail.example.com resolves to a different IP address.

# dig +short webmail.example.com
203.0.113.2

Resolution

Note: After applying the changes in a DNS zone, it might take up to 48 hours to propagate the changes on global DNS servers