I work as a mail carrier. Trust me, your mailman couldn't care less what you get in the mail. I have 556 people on my route. If I had time (which I don't) to mull over every single package everyone gets, I'd never get anything done. I deliver between 50-100 pkgs a day.
Mail carriers are not supposed to notice nor tell to anyone what you recieve in the mail. If they mention it to you, it's likely they're just trying to make conversation and be nice, not nosey.
We don't "tattle" on people, tell the "feds" or any other such nonsense I see on here from time to time. Postal inspectors have much bigger fish to fry than someone buying a few hundred pills off the internet. In fact, in all my years at the Postal Service, I've never even seen a Postal Inspector.
Once, in a small town I worked at, a man and his mother (yes, I said his MOTHER!!) were mailing home grown pot in boxes big enough to hold a tv. How did we know? Even we have a sense of smell. It was brought to the attention of the Postal Inspectors by telephone by a postmaster. Their answer was, "If it's not ticking, don't call us."