With physical mail and unwanted calls, it's easier to get yourself off lists. You can pretty much be assured that you're getting those letters and calls from US Companies (for those in the US). Therefore, they all fall under the jurisdiction of US Law.
Spam is not so easy. Even in the US, there are few laws which dictate mass emails, especially nationally. In a few select states (California I know of specifically), email ads have to follow very strict rules. The problem is that spam is international. Pakistan doesn't have to follow the rules and can truly spam however they want. The industry has terms for all this too. There's true spam, and then there's mass email marketing. Spam is the worst, using harvesting bots and other nefarious methods of getting your email address. Mass email marketing is legal in California if it's done right.
I used to work for an internet marketing company, we had to know the rules. In several states, the email addresses generated must be found by means of signups. This doesn't mean it's any less nefarious, but at least there's some interaction required on your part. You have to sign up for something with your email, like a free site or a giveaway of some sort. Your email address is then put into a database, used, and oftentimes sold in bulk. All this is totally legal. You should have read that End User License Agreement!
Legitimate emailers don't want useless addresses any more than you want to get junk email. They honestly are useless to them. If you unsubscribe to a legitimate emailer, they will take you offa list. Further, most companies will actually "scrub" their lists and create "scrub" lists for their partners, telling them that these are worthless addresses. Any company that knowingly adds the addresses on the scrub list is committing a crime.
Also, addresses are given different values depending on how they are acquired. If you are somehow tricked into giving an emailer your address, it's nearly worthless. This is "opt-out" and does not signify that you're actually interested. On the other hand, if you have to make a specific effort to sign up for something, it's considered "opt-in" and worth considerably more, especially if you fully understand what's going on.
As for what they can or can't do as legitimates? Anything with adult content must be marked in the subject line, very explicitly. Spam detector avoidance methods (fr33 v14gr4, ect.) cannot be used. The company from which the emails originate must say who's sending it. The company MUST include a visible method of unsubscribing. All these rules, when broken, can lead to very hefty fines.
There's a lot more to it, but the fact is, the ones who are just randomly hammering your inbox are likely not going to give up because you ask them to stop. They'll say "Oh, sure, you're unsubscribed" then sell your address to 50 other companies in a list of millions. Sadly, no laws protect us against that for the most part and few people will ever know what company it originated from.
It's a bane we have to live with. Even if the US had national laws regulating spam, thus making legitimate marketing all the more difficult in the US, we'd still have international spammers. There is no end in sight.
---
Do you want ants? Because that's how you get ants.
