I'm using a similar technique, but rather generating a random address @my-domain. To know which provider it was (in case I later get spam from somewhere else),

I'm using a similar technique, but rather generating a random address @my-domain. To know which provider it was (in case I later get spam from somewhere else), I keep a text-file + email myself any time a new forwarder is set up, so this way I can always look up which service it was. This way, I was able to spot a leak at box.com and maybe a couple of other places, before it was even announced.