Lots of 'bayes_toks.expireNNNNN' files in the bayes_path directory

Is that directory set to use a sticky bit? check with 'ls':

ls -la /path/to/directory
total 47576
drwxrwxrwt  1 root   root        8192 2004-08-23 17:26 .
[....]
-rw-rw-rw-  1 calum  calum       4155 2004-08-23 17:26 bayes_journal
-rw-rw-rw-  1 nobody nogroup  2584576 2004-08-23 17:26 bayes_seen
-rw-rw-rw-  1 root   root    10244096 2004-08-23 17:26 bayes_toks
-rw-rw-rw-  1 brian  brian    5255168 2004-08-23 15:58 bayes_toks.expire13091
-rw-rw-rw-  1 calum  calum    5255168 2004-08-23 16:08 bayes_toks.expire13925
-rw-rw-rw-  1 calum  calum    5255168 2004-08-23 16:14 bayes_toks.expire14454
-rw-rw-rw-  1 calum  calum    5255168 2004-08-23 16:29 bayes_toks.expire14922
-rw-rw-rw-  1 calum  calum    5255168 2004-08-23 16:36 bayes_toks.expire15160

If the "drwx" string ends in a "t", the sticky bit is set. That can cause complications, as described in this Debian bug.

If SpamAssassin is running using different user IDs, but sharing the same Bayes database files, it needs to be able to rename files in this directory. Using the sticky bit means that user ID 'X' cannot move files created by user ID 'Y' -- hence the write fails, and SpamAssassin has to give up the expire operation, logging an error.

The fix is to remove the sticky bit:

  chmod u-s /path/to/directory

You may want to investigate a way to lock down that directory, rather than leaving it at mode 0777, but that's outside the scope of this FAQ entry.