You can send kd neither emails nor letters. Right now there isn't even an address. But even if there was she wouldn't read them She has said on various occasions that she doesn't read fan mail at all.
She used to check out her official message board in the past but says she doesn't anymore. Yet posts on the AD board have a better chance of being read by her or her staff than those on non-official boards like this one, that's for sure.
You want personal contact? Go to her shows. You can give her gifts before, during or after the concert. You might meet her at the soundcheck or before she drives off at night. She may sign stuff for you and say a few words. She's great in person, so gracious and beautiful. It'll be a moment you will never forget.
Good luck!