function validateEmail(email)
{
    var emailpat=/^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,4})$/; 
    var matchArray=email.match(emailpat);
    if(matchArray==null)
     {
        return false;
     }
    return true;
} 

if(document.getElementById("txtYourmailId").value!="") 
	{
		if(!validateEmail(document.getElementById("txtYourmailId").value))
		{
			alert("Invalid Email Address");
			 document.frmpostresume.txtYourmailId.focus();
			return false;
		}
	}