read receipts + link tracking. if you use it for work, it's incredible. all the other solutions are heavy-handed CRM style plugins for gmail. canned responses

read receipts + link tracking. if you use it for work, it's incredible. all the other solutions are heavy-handed CRM style plugins for gmail. canned responses + simple mail-merge style things downside: because it's not gmail, search is...not as good as gmail. nothing is.