I think I've stated this here before, every casino should copy from what stake did when they updated their terms and conditions, they lock all their users out of their accounts, that is, you can login to your account by-pass the accept new terms and condition pop up which cover the whole screen, that is, stake forced all their users to make sure to read and accept the new terms before they are allowed access into their account proper, this is the best strategy, much better than sending emails, with this strategy, even though I personally believe that many gamblers are still going to accept the updated terms and conditions without reading it, I still believe this is much better than sending emails which users might not even take notice off, or will allow to sit there for several days or weeks without opening it, and some have trashing system which trashes mails in the inbox that have not been read for a set period of time.
You are right, if the top casino will notify the update of the terms and conditions with several strategies so that all users are aware of the updated TOS of the casino that has been changed or has been added other points, the most effective way is to announce in the pop-up information after the user has logged in to his account and the casino must send a notification to the user's email so that changes to the TOS are not debated in the future, but if the casino fails to change the TOS to the detriment of gamblers and the casino will not publish information on changes to users so that the casino blames users for ignoring the TOS.