Now that I've had to administer an email system (I installed Exchange over at Regal Air), I've spent a bit more time thinking about spam -- by necessity. Regal was getting their mail filtered through SeaNet, but for a myriad of reasons -- and I don't want to debate the choice -- we brought in Exchange. Almost immediately the users started complaining about the number of Unsolicited Commercial Email (UCE, or SPAM).
Microsoft supplies a plug-in for exchange they call the Intelligent Message Filter (IMF). This gizmo reads incoming mail, and assigns a SPAM value to it of zero to nine. Zero being the least likely to be SPAM and nine being most certain of being SPAM. I installed the plug in and started monitoring. Within a day I discovered that over half of our incoming mail was a seven or greater. I started the filter out at discarding anything seven or above. Within two days I had moved the filter level down to five.
As an idea of scale, prior to the migration, Regal had about 10 addresses. Four of those receive the bulk of the SPAM. Over the weekend, those four addresses got 700 SPAM email, and about two dozen legitimate mail.
Years ago, I created an account at Yahoo mail. This is my "business" address. If I buy something on line, register a product, or post on a public forum, this is the address I use. The Yahoo accunt recieves nearly 1,000 spam a month.
When the "dot info" TLDs came out I bought a vanity domain for my "personal" address. My registrar offers free mail redirection; so I created the address I wanted at my vanity domain, then have it redirected to my gmail account. This is the address I give to my friends.
A couple weeks ago, I started "Mistaken ID" as a blog of mail sent to me at gmail because someone gave out my address as his or hers. Apparently I don't get enough SPAM, so others are signing me up for extra. Anything addressed to my gmail account is probably junk. Which lead me to start reviewing what was being sent to gmail address, junk or not.