I'm looking to create a contact list in my Outlook for Mac.
On Outlook, click on the People Icon on the bottom Left.
On the People screen, there should be a choice at the top for "New Contact List".
Name the List at the top and Double Click in the list to Add Email Accounts to it. You should be able to add them from the Outlook Address Book.
Once you have everyone added, Save and close it.
You should then be able to create a new email and use the name of the Contact List in the To: section to send to everyone included in the list.