If you are using e-mail field in your form, maybe you will be surprised one day, that email foo@bar will pass validation. Today I will explain to you why.
Webform: Add optional routable email check for email address element https://www.drupal.org/project/webform/issues/3173490
Drupal Core: Drupal email.validator service isValid accepts emails with no domain https://www.drupal.org/project/drupal/issues/2822142
RegExp solution
[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,}$
