Newsletters (aka, Bulk Mail, as it is called in the ACP) are manually sent by administrators so if you do not want to send these than you could ignore that altogether. By "newsletters", did you mean something else?
If you meant the digest notifications, you would simply remove the ability for individuals to receive emails in their notifications in ACP -> Members -> Notifications. Just be sure to use the button to apply that to all users, otherwise, it will just apply to new users.