<div id="userid" class="lm-login-item">
    <div class="lm-login-label">
      <label for="rcmloginuser"><roundcube:label name="mail" /></label>
    </div>
    <div class="lm-login-field">
      <input name="_user" id="rcmloginuser">
    </div>
  </div>

  <div id="pwdid" class="lm-login-item">
    <div class="lm-login-label">
      <label for="rcmloginpwd"><roundcube:label name="password" /></label>
    </div>
    <div class="lm-login-field">
      <input name="_pass" id="rcmloginpwd" type="password">
      <a href="#" id="showpass">Exibir</a>
    </div>
  </div>

  <p class="formbuttons">
    <input type="submit" id="submitloginform" class="lm-login-submit" value="Entrar">
  </p>
</form>

$(document).ready(function() {
$( '#loginform' ).validate({
  rules: {
    _user: {
      required: true,
      email: true
    },
    _pass: {
      required: true
    }
  },
});