I also don't believe that it's a fake e-mail. Like others have said, I've seen the exact same thing too many times both here and in my outside life to believe that he didn't get a letter exactly like this.
Dresden, it's not that certain animals can bond and others can't. I'll be the first to admit that horses certainly do bond to certain people. However, they don't bond like people, they don't bond like dogs, and they don't bond like cats, they bond like horses. The biggest problem people run into is when they try to make horses into something that they aren't.
People try to rationalize the horse's every action the way that you would with a human by attributing those actions to some human emotion like love, jealousy, or bitterness. Horses are horses, nothing more, nothing less. Expecting them to change their instinct or nature to fit our ideas of how they should act, feel, or respond is like asking a leopard to change it's spots. It's just not going to happen. That's exactly why you have to train them like a horse, not like a dog or a child.