I have had this issue with several items I have shipped recently and one that I have yet to receive. When it first occurred I filed an inquiry with the Post Office online. Going to my local post office didn't help, the manager there just told me that "the only way to make sure the Post Office actually receives your mail is to hand it to them". I had dropped it in one of their drop boxes right outside the Post Office!! Gee, that makes me feel really warm and fuzzy about the service they are providing! Turns out my local post office never scanned the item, so no tracking was provided until it was dropped off at my customer's address....since then I have had to make about 6 inquiries, which I think makes them go and find the package and scan it through just to get you off their backs!! I know that my local hub in Phoenix has semi trailers full of mail waiting to get scanned in, it was verified from a local postal employee. I have had items waiting at that depot for up to two weeks to go out and it seems like the only way to get the packages to my customers is to make an inquiry through the USPS website. Hope this helps!
