Drupal 7 Ubercart 3.4 emailing order invoice action is not working

Here is my system settings: Drupal 7.20 Ubercart 3.4 Rules 2.2 All the other emailing function on this site are working properly except the ubercart emailing (order notification emailing and order status update emailing). The issue here is that the system is not sending order invoice after payment's done.

I tried to add another action that fired by the same event which is named "Customer completes checkout" by default, using "Send mail" action as the image shows below.

The test result is that system did the first action but never did the second. Tried to look at the watchdog, there is no message showing system was trying to send the order notification, and no error, but it did show the sent email of the one I added for the first action.

Anyone has met this issue before?

Any thought will be appreciated!

Did another test, previously using smtp 7.x-1.0, I went backward to smtp 7.x-1.0-beta2 and it worked...