Save your friends email address in your contact list (address book) under their name (with their number).
While in the "sent to field" just type the contacts name as it appears in your contact list (address book). It will add their email address in the field.
It will show as their name. Hover over their name and hit 'Q' if you want to see the email address.
That's the fastest way i know of.
bish0p34 is correct.
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