// Java Document
function checkform()
	{
	 if (document.contactus.txt_name.value=='')
		{
			alert('Please Enter Your Good Name.');
			document.contactus.txt_name.focus();
			return false;
		}
	 else if (document.contactus.txt_email.value=='')
		{
			alert('Please Enter Your Valid Email Address.');
			document.contactus.txt_email.focus();
			return false;
		}
	
	 else if (!checkMail())
		{
			alert('We can\'t reply unless you enter a valid email address...');
			document.contactus.txt_email.focus();
			return false;
		}
		
	         
		// Everything's Okey
		return true;
	}
<!--Form Check Ends-->	

<!--Email ID Check starts-->
function checkMail()
	{
		var x = document.contactus.txt_email.value;
		var filter  = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9])+$/;
		if (filter.test(x)) {
			return true;
		} else {
			return false;
		}
	}