One thing, that usually come first when you setup a Virtual Private Server (VPS) is security and enabling ssh exposes you to some hack activity! Yep, internet can be a wild and scary place sometimes!
An email alert, when someone logs in to your server via ssh, can be pretty useful to track who is actually using your server! But Keep in mind that this trick is not enough to secure your server! And here you are more useful basic advices before seeing how to set up our SSH alert:
Layered security is the key!