How did spammers get my address?

• Stolen off a website: Spammers use address harvesting software to "spider" websites and extract any email addresses found in those pages. If you provide a contact address on your personal website or leave your address on the guestbook of a site, sooner or later it will end up on a spammer's list and you can't get off again. It will be resold to other spammers any number of times.
  If you want to prevent that, don't leave your address on other people's sites and don't provide a clickable link for mailing you on your own site. Instead, you can create a graphic representation (GIF, JPEG) of your email address such as this, which is fairly safe. A human can read it, a robot can not (hint: try cut & pasting it!):

  

• Resold by another spammer: Many websites gather addresses for providing services, such as mailing you or another person some file. Be very careful with such sites. While many are reputable, others will collect all supplied addresses and use them for spamming or for sale to spammers.
• They guessed it: Spammers combine common first names, surnames, initials and digits with mail domains. Often they will send millions of mails with such made-up names to a particular service provider, so that whatever names happen to be valid will make it through. This is called a dictionary attack. In other cases, spammers take the local part of known addresses (the part to the left of the '@' character) and combine it with another domain name (the part to the right of the '@'). If there is a janedoe42@msn.com, maybe there's also a janedoe42@aol.com?
• Stolen off the usenet: If you use a newsreader to post in newsgroups, spammers may harvest the address you use there. Many people use non-replyable (fake) email addresses for usenet postings. A common trick is to insert "nospam" in the name (john.nospam@example.com intead of john@example.com). Spammers know this and often strip out the "nospam" part. Clever people have taken advantage of this by creating a valid address including nospam which they use for Newsgroup postings. Spammers strip out the nospam part, breaking the valid reply address :-)

Why does someone send me emails that I don't want?

Because spamming is profitable and too little is done to stop it. The costs of advertising a product via spam are so low that even if only a tiny fraction (say less than 0.01%) of the recipients buy the product, the spammer still stands to make money. Annoying the other more than 99.99% of recipients is of no concern him. Spammers often use resources stolen from other people (such as computers compromised by "trojan horse" type viruses) or get shielded by corrupt Internet service providers in foreign countries. That makes it very difficult to prosecute them.

In many countries there are no effective laws against spamming. US laws against spam are much weaker than laws passed in EU countries.

How can I unsubscribe from spam?

I was defrauded by a website on your list. What can I do?

When you purchase online, it is a good idea to do your due dilligence checking *before* you place an order. At the very least, do a Google search. Don't buy from spammers. Spam is criminal in many countries and unethical in any case. Why should you entrust the content of your wallet or your credit card details to a company which, by virtue of spamming millions, has already displayed unscrupulous behaviour? Even if you ignore that the profits from your order will pay for more spam, you yourself can become a victim. Many websites advertised via spam are hosted in countries beyond the jurisdiction of the courts in your country. Many such websites disappear within days or weeks. What are you going to do when you have a problem?

Help! A spammer is sending spam with my email address!

Sending spam with a fake sender address is a felony under US Federal Law (CAN SPAM ACT of 2003). Many of the spams sent with fake sender addresses involve other illegal activity, such as credit card fraud, intellectual property or trademark violations (software piracy, fake luxury watches, etc), illegal pornography, etc.

In such cases the domains advertised in the spam emails tend to be registered using fake postal addresses and often are paid using stolen credit card data. Servers tend to be hosted overseas, such as in Korea or China and often the spam is sent via trojaned third party computers.

In other words, you're dealing with professional criminals who are very good at concealing their identity. You will not be able to sue them. You won't even know where or who they are. But here is what you can do:

I received an email promising millions of dollars / euros / pounds. Is this a scam?

I have a scam email from an address that's not on your list. Can I send it?

Where can I submit a domain name advertised in spam that I received?