Email addresses are incredibly complicated. Here's a sample regex that will match every RFC822-valid address:
http://www.ex-parrot.com/pdw/Mail-RFC822-Address.html
You'll notice that it's probably longer than the rest of your program. There are even whole modules for Perl with the purpose of validating email addresses. So you probably won't get anything that's 100% perfect as a regex while also being readable. Here's a sample recursive descent parser:
http://cpansearch.perl.org/src/ABIGAIL/RFC-RFC822-Address-2009110702/lib/RFC/RFC822/Address.pm
but you'll need to decide whether you need perfect parsing or simple code.
