It’s easy to send a message to a number of people if you want to let all recipients know who else the message is going to: just use the cc: area.
But if your message goes to people who don’t know each other, and have no need to know each other or their email addresses, then use the bcc: (blind copy) area. And just send the message (to:) to yourself.
Quick tip: Are you prone to accidentally hit the “send” button before you finish a message? Then don’t fill in the to: box until just before you’re ready to send.