There are a few ways to do this, and it depends a bit on why you want to do it. If you are in development, and just want to ensure that no users get emails while you’re working on stuff, I highly recommend Postman SMTP. You can configure it so that all emails get logged, but not actually sent. It’s very useful for troubleshooting and for protecting your users from accidental mail. But with the ability to still see what “would be” sent, if you were live.
If you have a different goal — like just eliminating the sign up or activation emails, that’s a different thing. If you post up a bit more detail, I’m sure you’ll get the info you need. 🙂
