diff --git a/lib/google/appengine/api/mail.js b/lib/google/appengine/api/mail.js
index dd0995f..3dbbbde 100644
--- a/lib/google/appengine/api/mail.js
+++ b/lib/google/appengine/api/mail.js
@@ -42,14 +42,62 @@ EmailMessage.prototype.toString = function () {
     return this.body || this.html;
 }
 
+/**
+ * Determine if IP address is valid. Allows square brackets.
+ * @param {String} address IP address to check.
+ * @returns {boolean} True if the IP address is valid.
+ */
+function isIpValid(address) {
+    var parts = address.replace(/[\[\]]/g, '').split('.');
+    for (var i = parts.length; i--;) {
+        if (isNaN(parts[i]) || parts[i] < 0 || parts[i] > 255) {
+            return false;
+        }
+    }
+    return (parts.length == 4);
+}
+
 /**
  * Determine if email is invalid.
  * @param {String} emailAddress Email address to check.
  * @returns {boolean} True if the email address is valid.
  */
 exports.isEmailValid = function (emailAddress) {
-    // FIXME: implement me!
-    return true;
+    var parts  = emailAddress.split("@");
+    var local  = parts[0];
+    var domain = parts[1];
+    
+    var localValid  = false;
+    var domainValid = false;
+    
+    /**
+     * The local-part of the email address may use any of these ASCII characters:
+     * - Uppercase and lowercase English letters (a–z, A–Z)
+     * - Digits 0 to 9
+     * - Characters ! # $ % & ' * + - / = ? ^ _ ` { | } ~
+     * - Character . (dot, period, full stop) provided that it is not the  
+     *   first or last character, and provided also that it does not appear
+     *   two or more times consecutively (e.g. John..Doe@example.com).
+     */
+    if (/^[a-z0-9!#$%&'*+/=?^_`{|}~.-]+$/i.test(local) 
+     && local.charAt(0) != '.' 
+     && local.charAt(local.length-1) != '.'
+     && local.indexOf("..") == -1 ) {
+        localValid = true;
+    } 
+    
+    /**
+     * It must match the requirements for a hostname,
+     * consisting of letters, digits, hyphens and dots.
+     * In addition, the domain part may be an IP address 
+     * literal, surrounded by square braces [192.168.2.1]
+     */
+    if (/^[a-z0-9-.]+$/i.test(domain)
+     || (/^\[[0-9.]+\]+$/i.test(domain) && isIpValid(domain))) {
+        domainValid = true;
+    } 
+    
+    return (localValid && domainValid && parts.length == 2);
 }
 
 /**