/usr/home/mena/mail/new_haikuThe qmail naming convention is such that the name of the file can specify a unique email address for processing, which is exactly what I was looking for. Qmail rules for the email address email@example.com would be in a file named .qmail-example:com-joe — not exactly intuitive, but easy enough after a few tests.
And then, just like that, it was working: I can now email a haiku to a specific email address and expect to see it added to my archive in the space of a minute or two. I didn't use puppet after all, but I combined my two shell scripts into one more efficient one, learned that sed on BSD (used by my ISP) isn't the same as sed everywhere else, and above all found a simple solution to a lingering problem.
So that's it — the anti-climactic conclusion of an ambitious project — although I have a feeling I haven't run out of things to puppetize at home. Has anyone seen the dog?