JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-3.1.1.js"></script>
<form id="registration">
  <input type="email" required>
</form>

JavaScript

$('#registration input[type=email]').on('blur', function () {
	let email = $(this).val();
  
	if (email.length > 0
  && (email.match(/.+?\@.+/g) || []).length !== 1) {
  	console.log('invalid');
  	alert('Вы ввели некорректный e-mail!');
  } else {
  	console.log('valid');
    alert('Вы ввели корректный e-mail!');
  }
});