Hi there. Xobni for Gmail is in Beta right now and although it does not do exactly what you are asking, Xobni does have a recommendation engine that does help

Hi there. Xobni for Gmail is in Beta right now and although it does not do exactly what you are asking, Xobni does have a recommendation engine that does help to solve this pain point. Once you start an email to someone, Xobni will identify and recommend the people you often email with that person - so, although there is no specific list you can select, Xobni takes a lot of the guesswork out for you. If you are interested in getting into the Xobni for Gmail beta, go here - http://www.xobni.com/waitinglist/gmailbeta/ http://www.xobni.com/waitinglist/gmailbeta/ and enter the following media code for priority access: XOBNI-BRITTON