How spammers get your email address
Spammers collect addresses in many different ways, including:
Guessing. Spammers use automated software to generate addresses.
Harvesting from websites. If an email address is embedded in a webpage, spammers can use spiders (similar to those used by search engines) to find them.
Online registration. If someone gives their email address to a dodgy website or one with a lax privacy policy, the site owner can sell the addresses to spammers.
From other spammers. It's possible to buy lists of email addresses by the million online.
So-called spam email cancellation services. These bogus services offer to block unwanted email but really collect addresses.