function isValidEmail(email:String):Boolean
{
    var emailExpression:RegExp = /([a-z0-9._-]+?)@([a-z0-9.-]+)\.([a-z]{2,4})/i;
    return emailExpression.test(email);
}

http://enva.to/e4ig6z

<p>When accepting input from a user through a form it is often necessary to validate data before allowing it to be sent to a back-end script. This is most true for email addresses as they are often the only point of contact between yourself and the user and are important to get right. The below function makes use of a regular expression to confirm the email is of a valid format.</p>

Email Validation

ActionScript 3