Unsolicited Commercial Email (UCE)
a.k.a. Spam
How do spammers get my mail address?
Your website. The blackhats have programs called crawlers (or spiders) which traverse the www space on the internet harvesting mail addresses from web pages.
Do you really need to publish your mail address(es)? Why not provide a contact form instead? You may even get more enquiries that way because not all mail programs understand 'mailto' links.
A more proactive (some may say aggressive) strategy is to provide hidden links containing many bogus mail addresses as explempified by wpoison.
Usenet posts. When you subscribe to a newsgroup make sure your profile munges your mail address. The classic example being my.name@NOSPAM-domain.com. Alternatively, or as well, use a mail address that you never use for anything else.
Your browser. Some web sites will have ftp-traps which will ask your browser to use your mail address to log-in. Make sure you munge your mail address in the 'my profile' manager or equivalent in your browser. Alternatively, turn off support for javascript.
To find out what your browser says about you, check out www.privacy.net.
The sources above generate the most spam in our experience, but for a more exhaustive analysis click here.
What is spam?
Spam is unsolicited mail from someone (some organisation) you don't already have a relationship with.
Personalisation is not the issue. Bulk email can be (and often is) legitimate communication. For example when you opt-in to a mailing list.
An opt-out mechanism does not make the mail legitimate.
What else can I do?
Be sure you know who you are giving your mail address to. Use different aliases for each contact you have doubts about.
Report it. Newcomers to spam wars will find a user friendly (but automated) spam reporting service at spamcop.
... and if you've really got the hump with blackhats, click here to exterminate spammers step-by-step.
Join in the fun at SpamBattle.com