I had some weird messages stuck in my qmail cur directory that were causing traces. Deleting those messages stopped the traces coming. The filenames were like "1194523619.1759.www.save:2," instead of like "1194523619.1759.www:2,". Note the old timestamps - this isn't a normal thing to have message files like that, they must be unusual somehow. I'm not sure what they mean, but when qmail was queried about the messages by spambayes imap it didn't get a good response back, just:
['1 (UID 39913 )']
This is in the __getitem__ function. Because of "if headers is None:" evaluating, the "BadIMAPResponseError("FETCH response", response_data)" exception triggered - killing off spambayes entirely.
I had to manually "rm" the message files to get it running.
I suggest it be refactored to be a bit more robust against such things? I say this as someone a bit in the dark though, I don't know what these "save" messages are and how they got there, and I'm not well enough versed in SMTP responses to say whether qmail is behaving correctly or not (it's listing them then subsequent failing to return full details for them - seems dodgy to me!).