When you are making an email and need to address it to multiple people who you need to look up in the Global Address Book, click on To:
Type all of part of a name in the box at the top, where you see I typed goodrich in the picture below and then click on the magnifying glass to the right of that to search (or hit enter).
Find the result you need in the list of results and click on it once, so it’s highlighted like my address is in the list (yellow selection) You can then click on either To, Cc, or Bcc down below to add them to one of those.
DON’T CHOOSE OK
Then type another name in the top box and hit enter to search again. Repeat the steps above, selecting the specific person from the results and adding them to the Message Recipients lines until you have everyone. Then hit OK