Some time ago I found a rather useful way to use my Address Book contacts – group them and when you type the name of the group in Mail.app address field, it is expanded to all the contacts. But the problem was that when a contact had multiple addersses, I could not determine which was to be used for the group automatically and if I wanted to write to a specific address I had to manually adjust, which I forgot rather often.
Edit Distribution List
Fortunately Address Book has a way to specify the default address for any group (or distribution list as it is called). Just right-click on one of the groups, as shown below and pick “Edit Distribution List…”
Now a window pops up that shows you the entire list and all of the multiple addresses for each card. Just skim through the list and highlight in bold the default addresses which should be used automatically for this list: