I go to my local PO daily.  I'm on a first name basis with most of the staff.  I hand them my pile of items they scan them in and leave the lodgment receipt in my PO box to collect the next day.  I take a photo of each as a record, because it shows I have lodged the item and it also shows the destination postcode.

Avoid lunchtimes and the last minute 430pm rush and you'll be fine

I would never ever consider sending tracked items without lodging them and getting that lodgment receipt