I have an alternate email address I used when I signed up for one of those Page-A-Day online calendars (don’t sign up for it!) and I’m positive that’s the source of the majority of spam I get (2-3 messgaes per day - usually for meds). Once in a while I’ll accidentally open one of the messages. On the few occasions I have, the "To: " address is not mine. It’s close but not exactly the same.
How am I getting the mail if the address doesn’t match?
It is called e-mail spoofing.. The protocols used to send e-mail are inherently insecure. It is very easy to send a message from anyone (george.bush@whitehouse.org) to anyone with special tools. There are two parts to the “To:” information. One is the actual recipient e-mail and the other is information that displays the receipient name (what you are seeing).
This is what Spammers do. I am a little suprised that you only get 3 or 4 a day. I get 30 or more a day but I have had my e-mail address since 1996. These things tend to build with time as your e-mail address propagates through SpammerLand. The only way to stop it is to get a good Spam blocker. Your ISP may have one you can turn on.
I use Thunderbird to retrieve my mail (from comcast). How would I implement a spam-blocker?
I use a whilelist spam blocker called Qurb (which costs $20 or $30). It starts by permitting receipt of mail from anyone in your inbox or your address book. Everything else goes in a special folder to be reviewed by you. It works well since I rarely get mail from someone unknown to me that I want, but if you regularly get desirable mail from strangers, you’re going to have to be careful in reviewing the filtered messages.
Thunderbird has a built-in spam filter. You have to ‘train’ it to recognize spam quite reliably - i.e. tell it when you get spam and it will do a pretty good job of recognizing it and similar next time. Check out the help pages.