ld is right,there's a script that does this thing.
Wanna hear a funny? I got a similar email some days ago from a big sponsor that said he saw my site on sextracker and they wanted to promote them....The funny is that the specific site promotes only them
Anyway, the truth is that i'm used to such kind of spams and i dont get mad neither i get annoyed. I have to exclude the pathetic spam i receive every few days about one of my domains that is not listed in 400.000 SEs! lol