According to Writer's Digest (can't remember what month), the writer (sender) of email and snail mail have all copyright, um, rights. In other words, if you wrote a book about with these bad querys in it, you'd have to obtain permission from the writer of the letters. By sending them to you, the writer doesn't give you rights.
Actually, if someone mails me a letter, it becomes my property. I can publish it without their permission, as you can publish my letters to you because they are yours.
A third party, such as a biographer or scholor however cannot publish letters to me without my permission thus some interesting episodes wherein permissions were not granted, or were withdrawn, and biographies had to be re-edited at the last minute.
This applies only to actual physcial letters sent to a person, not to things posted on a blog, for which I technically retain copyright, but yanno...copy at will, have at it.