How do I set up a distribution list in mail

Address an email message

You can send a message to one or more people, or to a group, and set options to make sure messages go to the intended recipients, and to help protect their privacy.

Use a group address

• If you regularly send messages to the same set of people, you can create a group for them in the Contacts app. Then just type the name of the group in the address field of your message; Mail sends your message to each group member at the email address specified in Contacts.
• To prevent individual email addresses from being shown when you send messages to groups, choose Mail > Preferences, click Composing, then deselect “When sending to a group, show all member addresses.”

The Contacts App is the Address Book. In Contacts, select File in the menu and then Create a New Group. Add members to the group by selecting a contact or contacts and drag them into the group you created. Once your members or there, go to Edit in the menu, and select Edit Distribution List and select the group you made. If a contact has more than one address, click on the address to use for that contact in the group.

In Mail, to enter the group name, click on the blue +Circle icon on the right side of the address field of a new message to select the group, or just type the group name in the address field to enter it.

Contacts application icon in the Dock. Open your application folder, and look for Contacts. Open it, set up your contacts in it.

Dock Icon

Contacts is a separate application from Mail. You can access contacts in a new message window as I've indicated before: