I just came across an insane code snippet to validate e-mail addresses, apparently derived from RFC 822. It is in the form of a Perl module that can be downloaded at http://www.ex-parrot.com/pdw/Mail-RFC822-Address.html. The Perl code is intertwined with just a little bit of regexp hell, and looks as follows: (?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\”.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t] )+|\Z|(?=[\[“()<>@,;:\\”.\[\]]))|”(?:[^\”\r\\]|\\.|(?:(?:\r\n)?[ \t]))*”(?:(?: \r\n)?[…