You're searching through address books? Why?

Have you tried just typing part of the name or address into the new message's address box?

You merge address books by selecting and then drag-and-drop from one to the other. Drop onto the target/destination book's icon at the left.

Thanks for your answer. So obvious I should have thought to try it.

I have acquired several address books due to migration from several different systems which I had for different purposes. Sometimes I can remember something about the person but not the exact name or address.

I, too, search my Address Books, not for sending new e-mail, but for finding those where I squirreled away an address. My Address Books are sorted by the part the therin named have in my life, and there is overlap.