Messages not being distributed

I just moved mail delivery for my domain from from server A to server B, and now messages sent to the lists on server B aren't being delivered.

Un/Subscriptions (with confirmations) and digests work, but when a message is sent to the list itself it just goes *poof* and disappears. No dead.letter files (that I can find), LOGABSTRACT is set to yes, but logging stops after the message is added to the digest folder.

Any ideas? Is this a known problem that's been seen before? I'm on RH 7.2 (kernel 2.4.9-31), procmail 3.21-1 (rpm) and smartlist 3.15. I installed smartlist using the procmail 3.15 source tree. Could the problem be with using a newer version of the procmail binary?

TIA, Steve