I have done validation using below woocommerce hook.add it in your active theme's functions.php file.
add_filter( 'woocommerce_checkout_fields' , 'custom_override_checkout_fields' );
function custom_override_checkout_fields( $fields ) {
?>
<script>
jQuery('#billing_email').on('blur', function() {
validationFunction();
});
function validationFunction() {
if(document.getElementById("billing_email").value!='')
{
console.log(document.getElementById("billing_email").value);
var re = /^([\w-\.]+@(?!gmail.com)(?!yahoo.com)(?!hotmail.com)(?!yahoo.co.in)(?!aol.com)(?!abc.com)(?!xyz.com)(?!pqr.com)(?!rediffmail.com)(?!live.com)(?!outlook.com)(?!me.com)(?!msn.com)(?!ymail.com)(?!att.net)(?!comcast.net)(?!facebook.com)(?!gmx.com)(?!googleemail.com)(?!hotmail.co.uk)(?!mac.com)(?!google.com)(?!mail.com)(?!sbcglobal.net)(?!verizon.net)(?!yahoo.co.uk)(?!email.com)(?!games.com)(?!gmx.net)(?!hush.com)(?!hushmail.com)(?!icloud.com)(?!inbox.com)(?!lavbit.com)(?!love.com)(?!hush.com)(?!pobox.com)(?!rocketmail.com)(?!safe-mail.net.com)(?!wow.com)(?!ygm.com)(?!email.com)(?!zoho.com)(?!fastmail.fm)(?!yandex.com)([\w-]+\.)+[\w-]{2,4})?$/;
if(re.test(document.getElementById("billing_email").value)==false)
{
jQuery('#error').remove();
jQuery('#billing_email_field label').addClass('wrongemail');
jQuery('#billing_email_field input.input-text').addClass('wrongemailborder');
jQuery('#billing_email_field').append('<span class="wrongemail" id="error" style="font-size: 14px;">Please Enter valid business email address.<span>');
jQuery('#billing_email_field label').removeClass('rightemail');
jQuery('#place_order').attr('disabled',true);
}
else
{
jQuery('#billing_email_field label').addClass('rightemailborder');
jQuery('#billing_email_field input.input-text').removeClass('wrongemailborder');
jQuery('#error').remove();
jQuery('#billing_email_field label').removeClass('wrongemail');
jQuery('#place_order').attr('disabled',false);
}
}
}
</script>
<?php
}
return $fields;
}
i bind the javascript blur event to email text field then check the email id enterd by user.