Is it legal to send large packages to someone by USPS without their consent? If I understand correctly, it is legal to send someone letters and small packages without their consent. Does this apply to large packages? Can I mail a refrigerator to a random address? (Don't worry; I'm not actually going to do this.)
Yes. It is legal to do this within reason, although U.S.P.S. packages are limited to 70 pounds (which would be a very small refrigerator). Generally speaking, however, you have no obligation to pay for a package that you did not ask to receive.
In the US, your experiment is problematic in several respects according to the CAN-SPAM Act of 2003 CAN-SPAM Act of 2003 - Wikipedia. You can legally send unsolicited email, as long as you have an unsubscribe link in the message, and you have obtained those email addresses in a legal manner. Your project is problematic because 1) you using emails from an online dump, which more than likely came from a spam harvester, and those emails were probably not legally obtained. 2) the subject lines (and content) of the emails you send will be deceptive, because you are trying to get people to click on the link to give you data on the people who respond while not telling them the true nature of the email. 3) you will be displaying your collected data in a public manner related to those personal email addresses, after deceiving those people to the nature of your emails, and this could possibly be illegal in terms of privacy outside of the CAN-SPAM Act of 2003. Beyond the CAN-SPAM Act of 2003, in order to send all of those emails in the US, you will need to use internet service provider, which will either be a commercial business, a government entity, or and an NGO. All of those will have terms of service which probably restrict sending mass unsolicited emails using their services. This will be a worldwide project and poses no threat other than being classed as a spam email.... Wrong. You will more than likely be violating many email and privacy laws and those of many interest service providers in all of those jurisdictions, and will open yourself up to both civil and criminal liability.
Not for normal correspondence There are laws that require a specified channel of communication for specific purposes such as a physical address for the service of legal notices, but there is no general requirement. How, or if, a company communicates with its customers about complaints will either be specified in the contract or up to the company to determine and advertise. For example, this site specifies “ will be deemed to have been duly given when received, if personally delivered or sent by certified or registered mail, return receipt requested; when receipt is electronically confirmed, if transmitted by facsimile or e-mail; or the day after it is sent, if sent for next day delivery by recognized overnight delivery service” - any other method of delivery (Whatsapp, Facebook, even their own chatrooms etc.) is not a valid method of service, if you use those methods, then legally, you have not communicated. So, if the company requires complaints to deal with by online chat, they can safely ignore any letter or email you might send them.
I did the Googling: Prior to the case described in this article, a notice was to be deemed served if the sender can sufficiently prove that the letter was properly addressed, pre-paid and posted. Law - Section 7 of the Interpretation Act 1978 The case made it clear that the same law also sets a condition, where if the letter was not received at said mailbox, or too late received, the notice is to be deemed not served. The receiver is not required to prove that the letter has not arrived in the mailbox. Also, if your mail has been tampered with, you should contact Royal Mail - they will perform an investigation and put your mailbox in order. I work with tenants and landlords, thus lots of official notices. In this practice, it's often a recommended action to follow up on a notice and make sure the receiver has indeed received and acknowledged the notice. I don't know if it's a legal requirement, but often in disputes (which go to arbitration by a 3rd party), if one party states they did not receive the notice and the other party can't sufficiently prove that they did everything in their power to contact and confirm the delivery of the notice, the notice is regarded as not served. I believe you cannot deny post. If it's in your mailbox, it's your responsibility to check and read it.
In the UK and USA (and I imagine other jurisdictions) there have been laws that explicitly provide for orders obliging entities to (A) provide access or information and (B) keep the order secret. For example, in the USA the Stored Communications Act, Fair Credit Reporting Act and Right to Financial Privacy Act authorise the FBI to issue National Security Letters (Wikipedia, EFF, EPIC, Lawfare). These are an administrative subpoena, without prior approval from a judge, for meta-information (e.g. phone numbers dialed or email recipients addressed but not the content) of communications relevant to national security investigations. They typically contain a non-disclosure requirement prohibiting the recipient of the NSL from disclosing its existence or the FBI's demands. There have been challenges on First Amendment grounds to the non-disclosure aspect but, so far as I'm aware, they have all ultimately failed. Some of their non-disclosure requirements may eventually expire under other laws. In response, so-called 'warrant canaries' (Wikipedia) have been developed (and gone a bit further than the original idea) - these are intended to allow entities to relatively passively warn of such an order having been received if not the detail of the order. However, they can be legally risky in that they might be seen by a court as trying to circumvent the non-disclosure requirement and therefore breaking it.
Do not throw away mail that is not addressed to you. If you receive misaddressed mail, write "Not at this address" on the envelope and put it in a mailbox, or give it to the mailperson (source: United States Postal Service - Reporting / returning misdelivered mail). Also, if you contact USPS they may redirect the misaddressed mail for you. 18 U.S. Code § 1702 - Obstruction of correspondence Whoever takes any letter, postal card, or package out of any post office or any authorized depository for mail matter, or from any letter or mail carrier, or which has been in any post office or authorized depository, or in the custody of any letter or mail carrier, before it has been delivered to the person to whom it was directed, with design to obstruct the correspondence, or to pry into the business or secrets of another, or opens, secretes, embezzles, or destroys the same, shall be fined under this title or imprisoned not more than five years, or both.
Would any offence be committed for: Having this on your person? Buying or selling this? Leaving it around for people to plug in to a computer? In the abstract, I don't think that this conduct would violate either Section 36 of the U.K. law or U.S. law, although, obviously, purposefully destroying a computer itself (i.e. actually using the device without the consent of the owner of the computer) would violate many U.K. laws and would also violate many U.S. laws at both the state and federal level. I also don't think that possession or buying or selling this product would be a crime absent some intent that it be used illegally, in which case there might be an "attempt" to commit a crime offense, or an offense that would make one part of a conspiracy to commit a crime. In the "leaving it around" example, there is arguably an intent to use it to harm another improperly, although the phrasing is ambivalent. While many statutes in the U.S. criminalize possession of burglary tools, or drug paraphernalia, sometimes with an associated intent element (although even these crimes often have an express or judicially implied intent to use element), I'm not aware of any statute that criminalize possession of tools for malicious destruction of property. So, if the tools aren't possessed or used in a manner intended as a step in the facilitation of a crime, I don't think that any law is violated. So far as I know, the U.S. does not have a counterpart to Section 37 of the British statute cited above (it isn't a terribly easy thing to search for to definitively rule out the existence of such a law because federal law has many uncodified crimes in unexpected statutes and there are many sets of state criminal statutes, not all of which are codified either). The example giving in the comments by @gnasher729 of possession of a hammer which could be used to do the same things that this object could be used to do is instructive. Arguably, this USB-like tool is more specifically targeted at malicious conduct. But, for example, when I used to work as a radio news reporter, we had a machine that was basically a high powered magnet that was specifically designed to destroy all information on magnetic media. This was, in part, so that it could be reused, but it was also so that confidential interviews wouldn't fall into the wrong hands once they were no longer needed, in much the way that one might shred paper documents. It isn't so implausible to think that a device like this one might be necessary for individuals or firms with national defense secrets embedded in their hardware and software to have on hand in order to destroy a sensitive computer in order to prevent a security breach, if necessary. In a case like that, leaving one of these devices around the office unlabeled might be negligent, but wouldn't have the intent necessary to be an intended crime. And, it is hard to imagine that the device itself, which seems pretty simple, would itself involve any technology that is a national security secret, so it probably wouldn't violate export control laws. Of course, possession, purchase or sale of such a specialized device, or leaving it around unlabeled would certainly be powerful evidence of an intent to use the device in a wrongful manner, and hence, of an attempt to commit a crime. Indeed, possession of such a device or purchase of one might very well be sufficient to establish probable cause to seize the device and arrest the person holding it on charges of an attempt to destroy a computer. But, this device would be merely powerful evidence of an intent to commit a crime, rather than something that is a crime to commit in and of itself. There are no international laws that govern this kind of thing. The only international laws applicable to individuals pertain to war crimes and nuclear and chemical weapons. Even then, most international laws direct member nations to adopt domestic laws on the subject rather than being self-executing.
If the sticker is not easily removable, it would likely fall under defacement of the mail which is illegal according to 18 U.S. Code § 1705 - Destruction of letter boxes or mail: Whoever willfully or maliciously injures, tears down or destroys any letter box or other receptacle intended or used for the receipt or delivery of mail on any mail route, or breaks open the same or willfully or maliciously injures, defaces or destroys any mail deposited therein, shall be fined under this title or imprisoned not more than three years, or both. They do not have the right to deface your mail while they are holding it for you, and just because it's not inside an actual mailbox because it doesn't fit is not an exception. However, that requires arguing that a sticker is actually defacement. If it can easily be removed, like a sticky note, then you likely won't win that argument. In fact, many universities which must handle mail services for students advise that rubber banding a note around the mail is acceptable, as is writing student information onto the mail. So complaining about the sticker would likely just cause them to attach it in a different way that does not qualify as defacement. You can't completely stop them from advertising their stuff, and it's really not much different than if they had gone around and put a door hanger on all of your doors.