var espacos = '                           ';
var parse_email = /^[a-z0-9.]+@[a-z0-9]+.[a-z]+.[a-z]?$/i;
console.log("foo.bar@gmail.com" + espacos.substring("foo.bar@gmail.com".length) + parse_email.test("foo.bar@gmail.com"));
console.log("foo.bar@gmail.com.br" + espacos.substring("foo.bar@gmail.com.br".length) + parse_email.test("foo.bar@gmail.com.br"));
console.log("foo.bar@gmail.com.br.br" + espacos.substring("foo.bar@gmail.com.br.br".length) + parse_email.test("foo.bar@gmail.com.br.br"));
console.log("foo.bar@gmail." + espacos.substring("foo.bar@gmail.".length) + parse_email.test("foo.bar@gmail."));
console.log("foo.bar@gmailcom" + espacos.substring("foo.bar@gmailcom".length) + parse_email.test("foo.bar@gmailcom"));
console.log("foo.bargmail.com" + espacos.substring("foo.bargmail.com".length) + parse_email.test("foo.bargmail.com"));
console.log("@gmail.com" + espacos.substring("@gmail.com".length) + parse_email.test("@gmail.com"));

/^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/

/[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?/gi

/^[a-z0-9.]+@[a-z0-9]+.[a-z]+(.[a-z]+)?$/i

"^[_a-z0-9-]+(.[_a-z0-9-]+)*@[a-z0-9-]+(.[a-z0-9-]+).(.[a-z]{2,3})$"

"^[a-zA-Z0-9_.-]+@[a-zA-Z0-9-]+.[a-zA-Z0-9-.]+$"

<script type="text/javascript">
function validateEmail(email)
{
 var reg = /^w+([-+.']w+)*@w+([-.]w+)*.w+([-.]w+)*$/
 if (reg.test(email)){
 return true; }
 else{
 return false;
 }
}
</script>

function validEmail(email){
    return /^[w+.]+@w+.w{2,}(?:.w{2})?$/.test(email)
}

[A-Za-z0-9\._-]+@[A-Za-z0-9]+\..(\.[A-Za-z]+)*