Always nice to find your backup-mx spammed to hell:

messages in queue: 582749
messages in queue but not yet preprocessed: 427364

(sample)
After a little research, (read: google) I found the following link, giving a few more hints:
http://www.spamvrij.nl/lijsten/bedrijf.php?idbedrijf=1189
If that’s correct, then this could be our suspect:

Registrant:
J.J. Rams
Haardstedelaan 53
1271 NL HUIZEN
Netherlands

Administrative contact:
J.J. Rams
+31 (0)355261637
john-rams@bdg.centrin.net.id

.. which nicely corresponds to the -sending- isp/netblock. Oh well. Time for some asterisk-voodoo and a certain Monty Python song. ;>