After my spam filter has been inactive for more than two weeks, I finally had the pleasure to investigate what went wrong during the upgrade of my system to Debian Wheezy. Back then I took the conservative approach and kept my old configs when in doubt, especially when they were personalized to my tastes. Unfortunately DSPAM wasn’t so nice as to pass Exim any meaningful error message.
Long story short, the DSPAM package changed the location of its storage drivers. Inserting „x86_64-linux-gnu“ in the StorageDriver entry in dspam.conf solved the problem. Wouldn’t this be the first thing to look for when reading „transport returned 1 from command: /usr/bin/dspam“ in the mainlog?!