I cannot find a way to send email newsletters in bulk to my members. This is essential.
While there’s probably a better way, you could make a #newsletter category, set that category as default watching first post for all users, and then posting there would email everyone (assuming they haven’t explicitly disabled emails)
You can have all users watch a particular category that only you can post to, and they’ll get a notification when you post a new topic.
If you really want to email them a newsletter, then maybe you want to use an email service that is designed for that. If you use mailchimp you can use Discourse Newsletter Integration to manage the list with Discourse.