Starting from 3.0.0.0, Administrator can decide whether On-site and E-mail notifications are ON or OFF by default for new members. You can set that in the backend of your site. Navigate to WP Admin -> PeepSo -> Configuration -> Notifications

Available notification setting:

• Posts and comments
  • Someone commented on a Post
  • Someone liked my Post
  • Someone liked my Comment
  • Someone replied to my Comment
  • Someone shared my Post
• Profile
  • Someone liked my Profile
  • Someone wrote a post on my Profile
• Mentions
  • Someone mentioned me in a post
  • Someone mentioned me in a comment
• Messages
  • Someone sent me a new Message
• Friends
  • Someone sent me a Friend Request

Disable All E-mail Notifications for a Single user

Administrators can disable ALL e-mail notifications for a given user. You can set that in the backend of your site.
Navigate to WP Admin -> Users
Click Edit user you want to disable their E-mail notifications and then find: Unsubscribe this user from all e-mail notifications
Click, and that user will have their e-mail notifications disabled.