$email = $_POST['email'];
if(preg_match("~([a-zA-Z0-9!#$%&'*+-/=?^_`{|}~])@([a-zA-Z0-9-]).([a-zA-Z0-9]{2,4})~",$email)) {
    echo 'This is a valid email.';
}
else{
    echo 'This is an invalid email.';
}
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