While the Address Book is a simple and often efficient means of finding email addresses there are alternatives that may prove useful to some users.
Open a New Email.
In the "To..." field enter any portion of the recipients first or last name.
Tap Ctrl/K (Ctrl key and K key at the same time).
A list will appear of possible recipients from both your contacts and the Global Address Book which you can choose simply by clicking.
In the below image I have entered "ale" into the "To..." field in a new email.
I then clicked 'Ctrl/K" on my keyboard.
The list that appears includes everyone in the Address book (whether I have written to them previously or not) with ale starting their first or last name.