The default for max events is 10, which is a bit short for a normal SMTP
exchange. Expand it to 30 which should be large enough to keep most of
the traces.
We don't want to write debug messages to the log, but having them in
traces is always useful.
The traces are volatile and self-cleaning so the additional volume
should not cause any problems, and helps troubleshooting.
While at it, fix the depth constant when logging.
This patch reviews various debug and informational messages, making more
uniform use of tracing, and extends the monitoring http server with
useful information like an index and a queue dump.
This patch introduces the couriers, which the queue uses to deliver mail.
We have a local courier (using procmail), a remote courier (uses SMTP), and a
router courier that decides which of the two to use based on a list of local
domains.
There are still a few things pending, but they all have their basic
functionality working and tested.
