In Making Music Platform/Mailman, every actual mailing list is identified by an email address - a regular email address, such as members@mygroup.com. Any email sent to a mailing list's email address is automatically distributed to each person that is subscribed to that mailing list. This way, you only ever need to address an email to a single, simple email address in order to have the email sent to a large group of people.
Mailing lists can be configured in a variety of ways (see below). In the most common scenario, any person who is subscribed to a mailing list can send emails to that mailing list. So if the mailing list contained the email addresses of all your members, then any of those members can send emails to all other members. This may not be the desired behaviour, and if so, this can be easily changed. A mailing list of supporters/friends, or other non-members of your organisation, is an example of a mailing list where you would not want everyone on the list to be able to send emails to the whole mailing list.
Also keep in mind that because a Mailman mailing list is a simple email address, anyone can send an email to that address - including non-members of your group or even spammers (if they know about the email address). There are options within each mailing list's configuration that determine what happens when someone who is not on the mailing list sends emails to the mailing list. Options include accepting the email (not recommended), silently discarding the email (also not recommended), bouncing the email back to the sender, or asking the list's moderator to decide (see Moderating a Mailman Mailing List, below).
