Since updating to 10.9, whenever I open Mail, it opens this window first. After clicking continue, it works just fine. All the e-mail is there, nothing odd about that. It's just the initial opening of Mail. I left the program open for a few hours in the background to download all mail, but no change. If I click Quit, the window will disappear, but Mail is still running (without displaying any e-mail). I am then unable to open anything within Mail. After a Force Quit of Mail, I'm able to open it again without issue, except the same Welcome window. Clicking continue opens Mail as normal. Any ideas?