This page describes how to configure James to catch every single email you throw at it and place each email into a single POP account. This allows you to connect an email client to the POP account and view every email that you are producing. This setup is very useful for testing a program that you are developing which generates dynamic emails. It's a great way to fine tune the results you're getting.
Configuring James as a catchall
For catching all locally-originated messages you can do this (tested and working):
<mailet match="HostIsLocal" class="Forward">
<forwardto>catchall@mydomain.com</forwardto>
</mailet>
For catching ALL messages sent to this server, this should work (you'll need to turn relaying on):
<mailet match="All" class="Forward">
<forwardto>catchall@mydomain.com</forwardto>
</mailet>