In Apple Mail.  Click on Mail → Preferences

Under the Composing section, click on the Configure LDAP... button

Click on the + button in the bottom left to add a new server

Fill out the Server Info window with the following information:

Name: EDIR

Server: edir.alaska.edu

Port: 389

Search Base: ou=people,dc=alaska,dc=edu

Then click Save, and close out of the preferences window--

You're Done!!

Using EDIR within MacMail is easy, simply start typing a name in the To: field and it will automatically start searching for you.