diff --git a/lib/index.js b/lib/index.js
index 751ab46..2a0496f 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -7,10 +7,13 @@ var _sendgrid2 = _interopRequireDefault(_sendgrid);
 function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
 
 var SimpleSendGridAdapter = function SimpleSendGridAdapter(mailOptions) {
-  if (!mailOptions || !mailOptions.apiKey || !mailOptions.fromAddress) {
-    throw 'SimpleSendGridAdapter requires an API Key.';
+  if (!mailOptions || !mailOptions.apiKey && !mailOptions.username && !mailOptions.password) {
+    throw 'SimpleSendGridAdapter requires an apiKey or username / password';
   }
-  var sendgrid = (0, _sendgrid2.default)(mailOptions.apiKey);
+  if (!mailOptions.fromAddress) {
+    throw 'SimpleSendGridAdapter requires fromAddress';
+  }
+  var sendgrid = mailOptions.apiKey ? (0, _sendgrid2.default)(mailOptions.apiKey) : (0, _sendgrid2.default)(mailOptions.username, mailOptions.password);
 
   var sendMail = function sendMail(_ref) {
     var to = _ref.to;
diff --git a/src/index.js b/src/index.js
index 68f584c..008f424 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,10 +1,13 @@
 import SendGrid from 'sendgrid';
 
 let SimpleSendGridAdapter = mailOptions => {
-  if (!mailOptions || !mailOptions.apiKey || !mailOptions.fromAddress) {
-    throw 'SimpleSendGridAdapter requires an API Key.';
+  if (!mailOptions || (!mailOptions.apiKey && !mailOptions.username && !mailOptions.password)){
+    throw 'SimpleSendGridAdapter requires an apiKey or username / password';
   }
-  let sendgrid = SendGrid(mailOptions.apiKey);
+  if (!mailOptions.fromAddress){
+    throw 'SimpleSendGridAdapter requires fromAddress';
+  }
+  let sendgrid = (mailOptions.apiKey ? SendGrid(mailOptions.apiKey) : SendGrid(mailOptions.username, mailOptions.password));
 
   let sendMail = ({to, subject, text}) => {
     return new Promise((resolve, reject) => {