Mmskuramoto, another weird spam destination

In the grand tradition of johnsmithsvt, we’ve started seeing spam for mmskuramoto. None of it has been allowed into the system, since it’s coming from a blacklisted IP, so I don’t know what flavor the spam is, but the attempts were surprisingly well-behaved: most spammers treat the 451 we return to blacklisted IPs the same as a 5xx error (they retry maybe once, maybe fifty times, right away, then give up); the mmskuramoto sender backed off the retries very nicely. So nicely, in fact, that I got the originating IP whitelisted and the alias added, just so I could see what the spam was. Unfortunately (or not, probably), they gave up after 14 tries, just a couple hours before they would have gotten through.
For those who care, the blacklisting setup has been modified somewhat since the johnsmithsvt post referred to above: all country-based blocking is done with, but most of the blocking ends up happening because of a bunch of Class A and B size blocks (virtually anything in apnic or south america). We still use,,,, and, and they contribute (especially zen), but it’s mostly the huge swaths of net that are blacklisted.