User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.4) Gecko/20070515 Firefox/2.0.0.4 Build Identifier: version 2.0.0.4 (20070604) In Tools -> Options -> Composition -> Addressing there is an option "automatically add outgoing e-mail adresses". I have several adress books. Thunderbird just checks if e-mail address is in selected address book. I think that it should check if e-mail address is *any* of address books. Reproducible: Always Steps to Reproduce: 1. Create at least 2 address books "Personal Address Book" and "Collected Addresses", for example 2. Go to Tools -> Options -> Composition -> Addressing 3. Check "automatically add outgoing e-mail adresses" to "Collected addresses" 4. Write mail to test@example.com 5. Open address book, move test@example.com from "Collected addresses" to "P.A.B." 6. Write mail to test@example.com 7. Check, test@example.com is in both "P.A.B." and "C.A.". 3. Actual Results: test@example.com is in both "P.A.B." and "C.A.". Expected Results: test@example.com is just in "P.A.B."