If one of them is one you told to take you off the list, the other three are probably just other names he uses - or other vermin he sold your "confirmed" addy to.
They move veryquickly.
Many "experts" do suggest having one email account for correspondence, and another "junk" account to use when some "questionable" site demands an email address. At least one reasonably reliable source says you don't need a "junk" account - you just make up something for the questionable ones. (Make it look reasonable though?)
Since the spammers use "guessing" quite a lot, it is recommended that you use a name on your "good" account that won't be easy to hit on just by putting in "common" characters. For a really secure name, you need to include at least one or two numbers, some alpha characters, and one or two "symbol" characters - although your friends may have a little trouble remembering something like j0hn1nkan#as -- .
The spammers also use crawlers to look for email addresses on any site they can get into. This is the reason it's recommended that you never "clear-type" your addy, for example on the 'cat. Mostly they look for the "@" that's part of all email addresses, and/or for anything with the "dot" in it. The dot is less commonly searched, since it appears so often in website names. So there's some protection in spelling out - like my example j0hn1nkan#asATjunkmailDOTcom. Clever people who want to reach you will usually figure it out, but the mechanical harvesters are a little more likely to miss adding you to their lists.
My own rule is never use my email address except with "trusted friends" or in the same places where I feel reasonably safe using a credit card (not too many).
And as a courtesy to your friends, DON'T give other people their personal email addresses and certainly don't post them anywhere unless you have the owners' permission (implied or otherwise). Business email addresses pretty much have to be made public, or you don't get much business; but the spammers don't usually hit quite as much on addys that look like a business. They're looking more for the "idiot" category of "client."