I've noticed that a substantial amount of spam that I receive doesn't make sense -- that is, I don't understand why spammers would even be motivated to
send such spam since there seems to be no gain to them.
For instance, a spam I received just now contained only the following ASCII text:
damps sonnet quaked.
cols merged gage.
sadism heroic silly.
libyan tannic pagan.
There weren't any URLs or tracking images as far as I can tell... just nonsense text. What's the benefit to the spammer? If there's no tracking image and no link to click... there isn't really anything the user can do other than be annoyed and delete it.
The only reason I could think of would be that they expect people to reply to the sender (to verify e-mail legitimacy), but that seems rather convoluted.
Unless some spammers just like to annoy people, rather than make money.
perhaps that email had something like an embedded image or javascript that could/would dial out to tell the spammer that your email address is active.
other tactics i've seen are the "unsubscribe to this email" links on blatant spam which are social engineering attacks to trick the unwitting into telling the spammers that yes, someone is home at this address.