And just from the minimal Dark Web browsing I've done, it seems like post offices are really only searching packages when they already have some reason to be suspicious, like contact from law enforcement. Truly random checks seem like an extremely rare occurrence.
A couple days later when he returned from work a post it note was left on his front door that said something along the lines of 'I think the post office got my address wrong and you may have received it, please call me.' He took the package and the note to the police.
When they tried calling the number they got a message saying that number was out of service.
This is not the case. It's a very heavy ymmv sort of situation. Eg, a post office I lived close to would scan 1 in 10 packages of mail through an xray, including random letters. They had a system that would randomly select from the line.
However, when it comes to USPS a warrent needs to be had to open the letter. Because of this if mail is caught with drugs in it, or suspected, from an x-ray, the mail suddenly gets "lost", because it's cheaper and easier than filing warrants all day. Especially given that the DEA cares about the seller far more than the buyer. If the package is large, but not like massively large, they might go out of their way to file a warrant and give a "love letter", where instead of the mail being delivered, instead a letter is delivered that says, "We know what you're up to. Knock it off." (paragraphrasing ofc)
Because they want the seller, and because anyone can frame anyone else by mailing them drugs anonymously, I've not heard of a case where someone who has receiving drugs by mail who has gotten arrested, with two exceptions: 1) Massively large packages, like multiple huge boxes or barrels worth. 2) I have seen a falling out where someones friend reported them for buying drugs online, and an arrest was carried out then, but due to the potential for abuse, the DEA leaves the buyers alone.
I would very much hope not.
[0] https://www.uspis.gov/wp-content/uploads/2019/05/USPIS-FAQs....
FISA (post 9/11 "national security" authorizing legislation) adds some exceptions
> Third, provisions in the Foreign Intelligence Surveillance Act of 1978 (“FISA”), as amended, 50 U.S.C. § 1801 et seq., specifically authorize the Attorney General to conduct physical searches of mall without prior judicial authorization in certain circumstances. Section 304(e) of FISA, 50 U.S.C. § 1824(e), provides that the Attorney General, under certain circumstances, may approve the execution of an emergency physical search of property, including property that “is in transit to or from an agent of a foreign power or a foreign power,” id. § 1824(a)(3)(B), so long as the Attorney General subsequently obtains an order from the Foreign Intelligence Surveillance Court authorizing the search...
https://www.rstreet.org/2014/11/19/yes-the-government-can-op...
Likewise, I've received one package that was opened and inspected. It came in a clear plastic bag along with a very short note stating that it had been inspected in accordance to <whatever laws they were>.
Senders probably don't usually stamp that on illegal shipments, and the post surely doesn't drop in a polite notification if they discover something illegal in there.
Unless someone forged the notice (unlikely, as you point out) some government opened it (it could also have been the government of the sender or any transit country). All those notices are the government voluntarily letting you know because someone in the government thought it would be better; if the FBI wanted to open a package because they vaguely suspected terrorism they could do it without needing to stamp the package or give any notice if they wanted.
https://www.uspsoig.gov/document/packages-suspected-containi...