You can have the cake and eat it too.
The other day I ordered a couple of books from Amazon. I got a shipment notice from them yesterday. Of course, being Amazon, the notice had every detail that I was looking for including an USPS tracking number
Since I was reading this email from my gmail account, on the right side there was an Ad from USPS but it was almost like a service. Here is the ad:
You click on the ad and it will take you directly to the landing page where your shipment is tracked. Of course, you can do that through Amazon too (but that would require you to login to Amazon and click again on a separate link.)
So, hats off to USPS for using this advertisements to serve!