Mastodon sometimes may send you emails when certain things happen on your account. You can switch off these emails by doing the following:
- Log in through your server’s website or through the web app
- Click on ⚙️ Preferences
- Click Notifications on the left of the screen (or on the mobile site click ☰ and then Notifications in the menu)
- UN-tick all the boxes in the section marked Events for e-mail notifications
- Click the Save Changes button at the top of the screen
This won’t affect notifications you get within Mastodon itself, it just switches off the emails.