What is the law regarding my reprinting someone''s email to me in my blog?

People often ask me to work with them using the "contact" form on my business website, and whether or not I do relates directly to the written quality of their email. I am considering reprinting and critiquing portions of some emails in an instructional blog. I would delete all personal or otherwise identifying information. (The headings would be something like, "What''s Wrong with this Email?" The text would be instructional, not insulting.) There is nothing currently in my "contact" page that gives me permission to reprint the emails, or alerts senders. Is this something I can do without violating the sender''s IP rights? Would it make a difference if I include a note on the contact page that says something like "By submitting this form you are agreeing to allow me to reprint your letter, etc.?" Thanks!