For each system service, you can choose whether to allow all incoming communications, deny all communications, or allow only communications coming from specific IP/network addresses.
To enable/disable access to a service on your Plesk server:
Switch to the Edit mode and click the icon that accompanies the service name
OR
Switch to the Edit mode and click the service name. Then select the required option (Allow or Deny) and click OK.
To allow access to a service from specific IP/network addresses: