Email Validation using JavaScript

<script language="javascript" type="text/javascript">
  function ValidateEmail(x)
   {
    var EmailExp=/^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$/;
    if(x.value.match(EmailExp))
    {
         return true;
    }
    else
    {
        alert("Invalid mail id");
        x.value="";
        x.focus();
        return false;
    }
   }</script>

<asp:textbox id="txtemail" runat="server" Onchange="validateEmail(this)">