Code:
<!-- Paste this code into an external JavaScript file named: validEmail.js**-->

function Validate_String(string, return_invalid_chars) {
**valid_chars = '1234567890-_.^~abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
**invalid_chars = '';
**if(string == null || string == '')
**** return(true);

**//For every character on the string.** 
**for(index = 0; index < string.length; index++) {
****char = string.substr(index, 1);************************
**** 
****//Is it a valid character?
****if(valid_chars.indexOf(char) == -1) {
******//If not, is it already on the list of invalid characters?
******if(invalid_chars.indexOf(char) == -1) {
********//If it's not, add it.
********if(invalid_chars == '')
**********invalid_chars += char;
********else
**********invalid_chars += ', ' + char;
******}
****}
**}
************
**//If the string does not contain invalid characters, the function will return true.
**//If it does, it will either return false or a list of the invalid characters used
**//in the string, depending on the value of the second parameter.
**if(return_invalid_chars == true && invalid_chars != '') {
****last_comma = invalid_chars.lastIndexOf(',');
****if(last_comma != -1)
******invalid_chars = invalid_chars.substr(0, $last_comma) + 
******' and ' + invalid_chars.substr(last_comma + 1, invalid_chars.length);
****return(invalid_chars);
****}
**else
****return(invalid_chars == ''); 
}


function Validate_Email_Address(email_address) {
**//Assumes that valid email addresses consist of user_name@domain.tld
**at = email_address.indexOf('@');
**dot = email_address.indexOf('.');

**if(at == -1 || 
****dot == -1 || 
****dot <= at + 1 ||
****dot == 0 || 
****dot == email_address.length - 1)
****return(false);
**** 
**user_name = email_address.substr(0, at);
**domain_name = email_address.substr(at + 1, email_address.length);******************

**if(Validate_String(user_name) === false || 
****Validate_String(domain_name) === false)
****return(false);******************** 

**return(true);
}




<!-- Paste this code into the HEAD section of your HTML document.
**** You may need to change the path of the file.**-->

<script type="text/javascript" src="validEmail.js"></script>
Nice easy way to validate email with JS.