Support

1. A very common source of spam is not spam at all. Somebody you know has gotten a virus (possibly through their email) and the virus is on their computer, sending itself to everybody in their address book. These emails often look like spam, but their main purpose seems to be to spread the virus.
2. Posting an email address in any place accessible via the web will get you some spam. As an example, I recently registered for an SNMP "Enterprise Number". In order to register, you must supply an email address. This email address gets published in a public list of "Enterprise Number contacts". Apparently, the spammers ("URGENT PROPOSAL" and "STRICTLY CONFIDENTIAL" are typical subject lines) know all about this list. I started getting these emails right away. In another example, I was selling my car. I created a new email address just for the ads. I put this email address in three places: An eBay ad, a classified ad on an enthusiasts site and a small web site I created. This new email address started getting spam right away and continued to get spam long after I sold the car and removed the ads. See http://www.t3city.com/tools/emailencoder/ for more information.
3. Registering a new .com domain gets you a good deal of spam sent to info@mydomain.com sales@mydomain.com, support@mydomain, etc.. I am not sure how the spammers are figuring out about the new domain registrations. I know they don't have a valid list of email addresses, because these addresses aren't valid for my new domain.
4. Signing up for anything at all. Not so long ago, my son registered to win a "free Spy Pen Camera". The spam was sudden and extensive. We never got the spam (mostly porn offers) to stop. We eventually had to change his email address.

Unfortunately, once an email address is on the spammer's lists, the only thing you can do is change your email address. Sadly, for email addresses like info@mydomain.com sales@mydomain.com, support@mydomain, there is nothing you can do - the spammers can just guess at these. So far, the spam for these addresses is not too extensive or offensive - mostly offers for logo design, "Re: Your marketing campaign", etc..