Sorry if I was unclear - on Scoutbook - at present - I’m not aware of a way native to the platform itself as yet.
Export or obtain a list of emails and bring them into a “mass email platform” or “email newsletter service” … This is the simplest method for now. Sending outside the platform opens many options for metrics and tracking.
Mailgun, Sendgrid, AWS SES and others offer back-end capabilities and would be easy to integrate in the platform; but not a near term option. These may also be used integrated to a website or similar service. Ping me directly if you have questions as answers from this point branch off in many directions.
However, a preferred consideration may be;
MailChimp, Mautic, and (ack) ConstantContact as these are just a few of many newsletter options - commonly used approach and there are favorable choices in most cases. Using the newsletter approach very closely matches most use cases however a mail list might also be an option. Off topic but again I’m happy to answer directly if you’re interested.