require 'mail' module Email def self.is_valid?(email) parser = Mail::RFC2822Parser.new parser.root = :addr_spec result = parser.parse(email) # Don't allow for a TLD by itself list (sam@localhost) # The Grammar is: (local_part "@" domain) / local_part ... need to discard latter result && result.respond_to?(:domain) && result.domain.dot_atom_text.elements.size > 1 end end