Users coming from cPanel are used to access their account via the
/whm URLs. Unfortunately Plesk’s login method is to access port 8443 which posts an invalid, self-signed, SSL certificate. As a result clients/visitors are usually scared to access such links, as all modern browsers block invalid SSL certificates by default or post big warnings.
The most easy fix is, as of this writing, to redirect port 8443 to Plesk hostname, which normally provides a valid SSL certificate and doesn’t uses a non-standard port. The client/visitor should simply access the
/plesk URL and get redirected to wherever necessary. Also this helps providers redirect
/whm to the new URL, pointing legacy users to the right place.