Dear lj. Dear bloody lj. I wondered why I was suddenly getting absurd amounts of spam again and all of it in multiples. Well, it's that (lj username)@livejournal.com address they give you. They gave their sponsors access to it et voilà.
So to circumvent it, go to admin console and enter set no_mail_alias 1 This does not stop comment notification, apparently, but I shall hope it stops my spam.