There are many different types of spammer. Here are some examples:
- Affiliates of vendors of products that can cause embarrassment (e.g. pills and porno). Such spammers get paid by commission on sales. Some of the products may be genuine; many are fake or of dubious quality. See Why You Shouldn't Buy from Spammers
- Criminal gangs intent on driving up the price of a stock. They will have bought the shares before sending the spam and then sell their shares when the price rises. This is known as "stock kiting" or a "pump and dump scam." See Pump'n'dump: it's all About the Timing, Baby
- Advance-fee fraudsters. They write pretending to have access to a large amount of money and need your help to transfer it to another country. They offer a percentage of the money for your help. Often originates in Nigeria. Also known as a "419 scam." See Evidence of 419 Scam Targeting Using Google
- Companies that don't respect unsubscribe requests. See ZD are Spammers!
- Companies that, after you sign up for newsletter "A" also send you information about topic "B." This is known as "List repurposing." See Techweb Spams me; Am I Impatient?
- Legitimate companies who have bought lists of email addresses in good faith from liars. They are told that the names on the list are willing to receive unsolicited email, but actually the list is just names harvested from Web pages or stolen from address books. Such companies should perform better due diligence, but often don't.