Feedback By "Push" vs. "Pull"
Determining the status of a letter can be achieved by "pull" or by "push":
Feedback by "pull"
In "pull" feedback, the client system (your server) initiates a call to query the status of a letter. PostalMethods is contacted with one of the query methods and responds accordingly. The client system needs to poll PostalMethods until a final status is returned. This may require multiple attempts.
"Pull" Feedback Retrieval Methods
Feedback by "push"
In "push" feedback, the PostalMethods system initiates a call to the client system only when the status of a letter changes. The developer can decide whether to receive feedback by HTTP POST, by SOAP callback, or by email confirmation. In each case, the developer can also indicate to which URL, endpoint, or email address, respectively, feedback should be sent. In "push" feedback, the PostalMethods system does not need to be polled repeatedly, and only one call is placed back to the client for each change of status.
"Push" feedback is defined through the control panel (and not set through a Web Service call). The following events can be set to trigger a callback.
"Push" Feedback Events
- On Error: an error which affects the whole request have occurred
- Ready To Be Dispatched: letters were processed and are now waiting to be delivered to the postal service
- After Dispatch: letters were delivered to the postal service
See Push Feedback specifications in the reference manual.