Merge pull request #2 from ChrisGrant/patch-1

Return after promise rejected.

Author: acinader

index.js

@@ -19,6 +19,7 @@ var SimpleMailgunAdapter = mailgunOptions => {
       mailgun.messages().send(data, (err, body) => {
         if (typeof err !== 'undefined') {
           reject(err);
+          return;
         }
         resolve(body);
       });