Personally, I think you're tilting at windmills. That said, I can offer a small correction to Ovid's post: RFC 822 has been superseded by RFC 2822. (Since the RFCs provide what looks like BNF for the actual address spec, I'd suggest using a parser-builder instead of a regex - I guess Parse::RecDescent and Parse::YAPP are pretty good, though I haven't used either. Parsers are worth learning about, too.)