Selection of the destination address from the address book could be made more efficient. In thunderbird the last addressbook used opens automatically in a sidepane of the compose window. A doubleclick on an entry copies that into the "To" field. Claws needs 5 clicks instead: 1. Open address book list 2. Select address book 3. Select address 4. Copy to the "To" field 5. Close address book
Have you tried CM's one-click version? Start typing the first few characters in the To: field and hit TAB... click on the desired address and you're done. Avoids your steps 1,2,4 & 5... :)
Further efficiency cannot be achieved until mind-reading hardware is available.