I buy postage and label online....before it prints you verify that you are not shipping anything hazardous and within their rules, etc/ Then I usually walk pkg out and hand it to the mail lady as she drives up to mailbox if I'm home. She never asks what it is. I shipped 2 receivers the other day in a small flat rate box and simply left it in box with flag up. I have a wireless alarm on my mailbox that goes off in the house when the door is opened, that will alert me when the mail arrives but also alerts me when mailbox is opened.
If not I leave on front porch and they have to get out of their little truck and come get it.
The post offices that refuse to ship barrels aren't following their own rules.