The logged error messages from submit and courierfilter into the syslog, well, suck.

Nov 18 18:28:49 mail submit: [ID 702911 mail.error] Permission denied

That's lovely... to what? In a system with many, many connections going back and forth, there are no ID numbers to link sessions (the 702911 stays the same), it's impossible to even try and troubleshoot this.

Nov 18 18:25:17 mail submit: [ID 702911 mail.error] No such file or directory

Again, what is it looking for?

Nov 18 18:25:54 mail courieresmtpd: [ID 702911 mail.error] error,relay=::ffff:131.216.23.83,from=<my...@cs.unlv.edu>: 432 Mail filters temporarily unavailable.

Ummmmm, OK... no error messages from courierfilter... no messages at all from courierfilter, actually... it's running, as are the filter processes, and I can send mail telneting into 25. Did the filter crash? Can it not communicate with the socket file? What's going on here?

Nov 18 18:28:39 mail courierlocal: [ID 702911 mail.info] id=000BC74C.3FB33A52.00004D17,from=<ro...@kerberos2.egr.unlv.edu>,addr=<michae lv...@egr.unlv.edu>: /usr/lib/courier/bin/maildrop: Unable to open mailbox.

This one at least I can guess what it's trying to open, but it still would be nice to have it listed.

Also, there are a number of errors in the courierfilter man page, or at least seem to be:

"For various silly reasons, the recommended implementation is to create /var/spool/courier/filters/.NAME or /var/spool/courier/allfilters/.NAME (after making sure that it doesn't exist) then rename .NAME to NAME."

If I have my filter create the lock in /filters/, it never gets called. It does under /allfilters/. Also, the paths given may not be correct, on the Solaris install here is /usr/lib/courier/var/filters, for example.

"The result code follows the same format as regular SMTP replies (even though the message may not have been received via SMTP), and can be used to communicate acceptance, temporary failure, or a permanent failure."

A little misleading - temporary failure and permament failure messages are relayed back to the client, but acceptance messages are not.

Just the results of a very frustrating day of beating head against desk trying to get a mail filter to work correctly...