There is a problem with Fan Mail, when you click on Fan Mail icon on the user avatar menu, it directs the mail to your blog, not the person you are trying to send it to. It only appears to be doing this on the Inbox.

I’ve disabled/uninstalled XKit, and the problem still continues, meaning it is a Tumblr-related problem, and not an XKit bug. They are probably working on fixing that. I can’t provide any help on this, sorry.