> 1. Messages with word salad or random quotation unrelated to anything in the
> subject line and body (what is all about?);
Beysian chaff, as explained, usually accompanied by an image file with the actual content. Interestingly, the text in the image files have been increasingly camouflaged in the manner of "enter this text" loopholes for web forms, presumably to foil attempts at optical character recognition.
> 2. Penis enlargement offers (how is that supposed to be performed over the
> internet?)
Porn sites. Duh. :-)
> 3. Prescription, sex performance or narcotic drugs offers (will I be grossly
> overcharged, get fake drugs, or nothing at all? - or perhaps a narc squad
> busting my door?)
I imagine at least some of them are quasi-legit if risky prescription drugs from abroad, or hrebal remedies, or flat out scams. If you've ever seen those Enzyte commercials with "Smilin' Bob", they turned out to be an elaborate credit card number harvesting scheme. They send you the free samples, but keep charging your card. Not spam, but I imagine that kind setup is typical.
> I presume that all of those are scams to fleece people in one way or
> another, but it is not clear to me how. Does anyone have any ideas?
You send money to them, and they send oregano in pill form, I guess. Many of the links that you see wind up leading to websites all over the world, so I imagine the chance of retribution is pretty small.
Another element is that it costs them next to nothing to send out quazillions of emails, and they only need a small percentage to respond to rake it in, and think we've all met people who'd respond, bless them.
A big thing recently has been pump-and-dump stock schemes pushed by people with apparently no relation to the companies in question. The spam is sent by hijacked PCs, so there's no way to trace it.
> Lo and behold, several days later I got an email from him regarding the
> "offer." I did not reply, but since then that account was inundated with
> similar scams, which made me thing that these guys must form some kind of
> network and share information.
I played one of these people by email for a while after they responded to a roommate ad of a friend's. I'm a hater player, you see. The course was, as you said, predictable. Of course, for a photo they sent a hot babe in a bikini. Like, OoooOO, *this* could be like _Three's Company_! They're pretty much automatic if you post anything on craigslist.
-- Andy