Email Validation class

email_validator.rb

require 'resolv'
require 'net/smtp'

class EmailValidator
  # Note that obsolete syntax support has been stripped
  Pattern = %r{
    # From RFC 5322 s 3.2.1
    (?<quoted-pair>     \\ [\x21-\x7e \t]){0}

    # From RFC 5322 s 3.2.3
    # NOTE: Omitting CFWS patterns
    (?<atext>           [a-zA-Z0-9!#$%&'*+\-/=?^_`{|}~\u007f-\uffff]){0}
    (?<atom>            \g<atext>+){0}
    (?<dot-atom-text>   \g<atext>+ (?:\. \g<atext>+)*){0}
    (?<dot-atom>        \g<dot-atom-text>){0}
    (?<specials>        [()\[\]<>:;@\\,."]){0}

    # Derived from RFC 1034 s 3.5
    (?<domain>          \g<label> (?: \. \g<label>)*){0}
    (?<label>           [a-zA-Z] (?: \g<ldh-str> [a-zA-Z0-9])? ){0}
    (?<ldh-str>         [a-zA-Z0-9\-]*){0}

    # From RFC 5322 s 3.4.1
    (?<addr-spec>       \g<local-part> @ \g<domain>){0}
    (?<local-part>      \g<dot-atom>){0}

    \A \g<addr-spec> \Z
  }x

  def email_domain_valid?(domain)
    Resolv::DNS.open do |dns|
      return ! dns.getresources(domain, Resolv::DNS::Resource::IN::MX).empty?
    end
  end

  def mailbox_exists?(address, domain)
    Net::SMTP.start(domain) do |smtp|
      smtp.rcptto(address)
    end
    return true
  rescue Net::SMTPFatalError
    return false
  end

  def email_valid?(address)
    match = Pattern.match(address)
    return unless match
    email_domain_valid?(match[:domain])
  end
end