Last night after updating to Mavericks and all else, I opened Mail and then couldn't close it. Couldn't find a way to force quit either, not in the right click menu anymore. This morning I still can't close it and the window keeps disappearing, have to hit command-0 all the time. So annoying. I have gmail and it didn't update until the second or third time I reopened the Mail window with command-0. So yes, eventually Gmail worked. Still won't shut down though.