Back when I was running a disposable email service called dodgeit.com I settled on a similar approach. I would just have postfix drop the mail in Maildir style files, then had a perl script parse the messages one by one. I didn't even call it from cron--it would just finish traversing then start over again after sleeping for a second. This effectively scaled to thousands of messages an hour on a single dedicated host.
I played around with a number of approaches, like the author here. But the one that just trusted the mail daemon to do its thing and the Linux filesystem to do its thing worked best for me.
I played around with a number of approaches, like the author here. But the one that just trusted the mail daemon to do its thing and the Linux filesystem to do its thing worked best for me.