Frankly, somebody who sues over an ordinary message might well get no damages, because the message has no commercial value, but if you want to stay strictly in the law, you should ask first. On the other hand, don't go nuts if somebody posts your E-mail. These days, almost all things are copyrighted the moment they are written, and no copyright notice is required. Copyright is still violated whether you charged money or not, only damages are affected by that. Postings to the net are not granted to the public domain, and don't grant you any permission to do further copying except perhaps the sort of copying the poster might have expected in the ordinary flow of the net.
Fair use is a complex doctrine meant to allow certain valuable social purposes.
Ask yourself why you are republishing what you are posting and why you couldn't have just rewritten it in your own words. The ownership of names is also from trademark law, so don't say somebody has a name copyrighted. Copyright law is mostly civil law where the special rights of criminal defendants you hear so much about don't apply. Watch out, however, as new laws are moving copyright violation into the criminal realm. Permission is granted to freely copy this document in electronic form, or to print for personal use.