email_regex.rb

email_regex = begin
      qtext = '[^\\x0d\\x22\\x5c\\x80-\\xff]'
      dtext = '[^\\x0d\\x5b-\\x5d\\x80-\\xff]'
      atom = '[^\\x00-\\x20\\x22\\x28\\x29\\x2c\\x2e\\x3a-' \
        '\\x3c\\x3e\\x40\\x5b-\\x5d\\x7f-\\xff]+'
      quoted_pair = '\\x5c[\\x00-\\x7f]'
      domain_literal = "\\x5b(?:#{dtext}|#{quoted_pair})*\\x5d"
      quoted_string = "\\x22(?:#{qtext}|#{quoted_pair})*\\x22"
      domain_ref = atom
      sub_domain = "(?:#{domain_ref}|#{domain_literal})"
      word = "(?:#{atom}|#{quoted_string})"
      domain = "#{sub_domain}(?:\\x2e#{sub_domain})*"
      local_part = "#{word}(?:\\x2e#{word})*"
      addr_spec = "#{local_part}\\x40#{domain}"

      Regexp.new "\\A#{addr_spec}\\z", nil, 'n'
end