Sending mail to a group of 800?

I'm a member of a hobby club with 800 members. We are talking about how to improve communication and email is one possibility. I am very aware that if I try to send messages to these people in bulk or even in groups of 50 I'll soon be shut down by yahoo as a spammer. However, I get messages daily from organizations that I've signed up for that must send out email to thousands. How do they do this? We want to do it legally, of course. Where do I start?