Correct me if I'm wrong, but Lamson enables those hooks/workers as well - but integrates with an FSM and a queuing mechanism (Celery) to get this done.
Additionally, there is Apache James (Java) which does something similar.
Additionally, there is Apache James (Java) which does something similar.
I'm not super familiar with Apache James, but it appears to be a mail server with pluggable components. Switchboard fits in as a layer between any mail server that supports IMAP, and its version of pluggable components [processes connection over the interface].
Thanks, this really helps us see where the documentation needs to be improved :)