There is no alternative to e-mail. Except perhaps for SMS. There is no other method for contacting people that is anywhere near as pervasive. It also has the ad

There is no alternative to e-mail. Except perhaps for SMS. There is no other method for contacting people that is anywhere near as pervasive. It also has the advantage of being federated, not controlled by any specific entity. Besides that, compared to WhatsApp and signal, email is generally for longer and less urgent messages. Those fit notifications much better. In that context an email saying "hey this is whats up, login as you normally do if you want to verify or act accordingly". It's far from ideal. We will probably come to some form of solution at some point. But at this moment it is a clear no-brainer.