I upgraded to Mavericks about a month ago. I had been happily using Gmail with Mail in Mountain Lion. I should have done my research before upgrading, but I didn't, so now I'm learning about the world of hurt that is Gmail + Mail. I just found out this week that emails I've been sending have not been going out and there is no record of them. Right now I can think of three emails that I wrote to three different recipients that apparently didn't show up in their inbox and don't show up in my Sent Items. This kind of sucks, mainly because I don't know what did and didn't get sent. I'm on 10.9.1. Maybe I'll just use Airmail for the time being.