class Net::POP3Command

def apop(account, password)
  raise POPAuthenticationError, 'not APOP server; cannot login' \
                                                  unless @apop_stamp
  check_response_auth(critical {
    get_response('APOP %s %s',
                 account,
                 Digest::MD5.hexdigest(@apop_stamp + password))
  })
end