submitted by Jen Flanagan...

- First is that unless you pay for express, registered, and other express services..  the post office doesn't actually offer "Tracking" on your package. So even though they do scan it in occasionally.. from what I am told.. they are not required to. (neither first class, parcel or priority offer "Tracking" although priority does offer confirmation. But confirmation is only to show it was delivered and they don't have to put any scanning information before that point.

- Since I am sure you have ordered online before I am thinking you must have noticed when a pkg is on its way that occasionally it will show "billing information received" and other times it shows it was "accepted" or "processed" .. and other times it will show absolutely nothing. Believe me when I say how frustrating this is for us (the company) because gals often get the wrong impression (which is NOT at all their fault) that when they see each of the different scans of these thinking that they have tracking because of this. It is only because the post office has chosen to scan these particular packages. I have noticed personally they scan them about 1/3 of the time. But it will depend on the particular post office too. They all seem to have their own "personality" so to speak on whether they scan or not.

Here is the information about tracking vs delivery confirmation..

(my writing will all be in purple any thing not in purple is from the USPS site)

As you know when you received your stamps.com notice it gives you a delivery confirmation number on there..

It should look something like this:

   Delivery ZIP............Zip here

   Shipment Date...........shipping date here

   Mail Class..............First-Class Mail

   Signature Required......No [or yes if purchased]

   Confirmation Number.....91010************ etc here..

According to their site the only way they will specifically track a package is if it is registered. 
I’ll highlight the part that caught my attention:

Can I track / trace First Class Mail?

Letters or packages sent via regular (First-Class Mail™) mail cannot be tracked or traced based on name and address.

Due to the large volume of mail moving through the Postal system each day, it is impossible to trace a single piece of regular, or First-Class, mail.  Only Registered Mail, which is accounted for during its entire journey, can be accurately monitored from location to location.  

Other products, such as Express Mail®, offer additional routing information as the mailpiece travels to its destination.  Extra Services can also provide final delivery status information.  For more information, go to the Track and Confirm Web site.

Yet I am guessing, like me.. you have definitely seen them occasionally track packages as they go from place to place. Though I know they don’t always do it. Why can’t they just be consistent??

So it is totally confusing to customers right? And the companies too!!

Check out this page I found on tracking:

Tracking provides detailed progress of Express Mail, Global Express Guaranteed, and Express Mail International packages while enroute to their destination.  Some of the statuses you may see when viewing your tracking information include:

• Acceptance - This scan means the package was received by the Post Office for mailing
• Arrival - This scan means that the package arrived at the Post Office for delivery
• Delivered - This scan means that the letter carrier has delivered the package to the location on the mailpiece

Notes:

        Regular mail, such as First Class Mail or Priority Mail cannot be tracked
        Items that are mailed from any international country may be trackable in that
           country but not here in the USA