The fetchmail log file is specified in fetchmailrc. When Trestlemail starts up, it reads the trestlemailrc file to tell it how to distribute the message. If the message is destined for a mailing list, Trestlemail removes extraneous headers, marks the message as bulk, reads the mailing list file, and sends a copy of the message to every subscriber to the list. Its task finished, Trestlemail exits and waits for Fetchmail to start it up again to deliver the next message. Debugging If unexpected things go wrong, it's not terribly easy to get information from Trestlemail.
Daemons lead a very non-interactive life.
If the catastrophe address is set up properly, trestlemail tries its best to send errors as E-mail messages. If it does exist, the error is appended to the log, but the E-mail message is not sent. All Perl and Trestlemail stdout and stderr appear in the fetchmail log. Development is actually pretty straightforward. You'll notice some debugging remnants throughout the trestlemail script.