You can take a look at the suggestions here:
But note that the email verification emails may not then send.
Users have a setting to receive no email for the activity summaries (under user > preferences > email).
Also, disable the activity summary emails, you can look at the disable digest emails site setting.
Emails are sent for many purposes: password reset, activity summary, PMs, chat messages, even replies to posts. I’m not sure if you can disable only certain things, though.