using addCallback before addErrback

due to the way how the add*back methods are implemented in Promise.js,
both the callback and the errback are fired in case of an error if the
errback is specified before the callback

lib/smtp/client.js

@@ -288,17 +288,16 @@ Client.prototype.data = function(data){
     var client = this;
     var promise = new Promise.Promise();
     this.beginData()
-      .addErrback(function(e){ promise.emitError(e); })
       .addCallback(function(){
         client.sendData(data)
           .addCallback(function(){
             client.endData()
-              .addErrback(function(packet){ promise.emitError(packet); })
               .addCallback(function(packet){
                   promise.emitSuccess();
-              });
+              }).addErrback(function(packet){ promise.emitError(packet); });
           });
-      });
+      }).addErrback(function(e){ promise.emitError(e); })
+;
     return promise;
 };