reject mails beloging to closed processes

the archive-process-email script is the thing that processes incoming mails to archive@nm.debian.org (the -XXX part is the "local extension").

To avoid loading the whole of django at each incoming mail, with a non-trivial risk of crashing and therefore losing mails, we should provide an easier way for that script to know what to accept and what not to accept.

The reason to do this is to:

• "lock" the process at the status when it's closed
• prevent spam from reaching closed process, since apparently spam mail can arrive several years after a process is closed (!)

I don't see any good reason to mail a closed process, but if there is one please tell me more :) - if there are use cases we might be able to build some kind of whitelist?

A simple enough way would be for the website to write the list of open processes in a file under data/, which would then be consumed by the arcihve-process-email script, and update that list whenever:

• a process is opened
• a process is closed

other implementation ideas welcome.