PHP Email Validation

email_validation.php

<?php

const VALID_EMAIL = '/^[a-z0-9!#$%&\'*+\/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&\'*+\/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+(?:[a-z]{2}|aero|asia|biz|cat|com|coop|edu|gov|info|int|jobs|mil|mobi|museum|name|net|org|pro|tel|travel)$/i';

function validateEmail( $email )
{
  if ( !preg_match(VALID_EMAIL, $email) )
  {
    return false;
  }
  return true;
}

$email_valid = 'test@example.com';
$email_invalid = 'testexample.com';

echo 'Email: '. $email_valid .' is: ';
if( validateEmail( $email_valid) ){
  echo 'valid';
} else {
  echo 'invalid';
}

echo '<br>';

echo 'Email: '. $email_invalid .' is: ';
if( validateEmail( $email_invalid) ){
  echo 'valid';
} else {
  echo 'invalid';
}

?>