email validation in js.html

<html>

<title>E-mail Validation</title>

<head>
	<script type="text/javascript">
		function mailchk() {
			var emailID = document.getElementById("mail").value;
			var regexp = /^[0-9 a-z A-Z]+(.|_)?[0-9 a-z A-Z]*\@(yahoo|gmail|colin|rediff)\.(com|in)$/;
			if (emailID.match(regexp)) {
				return true;
			}
			else {
				alert("Please enter correct email ID");
				document.getElementById("mail").value = "";
				document.getElementById("mail").focus();
				return false;
			}
		}
	</script>
</head>

<body>
	<form>
		<input type="text" id="mail" onChange="mailchk()" required>
		<input type="submit" name="save" value="save">
	</form>
</body>

</html>