Qmail-Updater

The problem with mkvalidrcptto is that it needs to be run every time you add or remove an email address from your server. A simple way to do this would be to periodically run mkvalidrcptto using a cron. While that would work, it's not that practical - a new email address added to your server won't function until that cron job has run. Run it too frequently and you waste processor time updating a file that probably doesn't need to be.

The onchange patch for vpopmail allows an external script to be run whenever it changes something. Configured as we installed vpopmail, that script would be /home/vpopmail/etc/onchange.

Rather than simply using the onchange patch to run the mkvalidrcptto script, we're going to set up a daemontools service called qmail-updater that will run mkvalidrcptto when it is triggered by onchange. I highly recommend you read John's page on qmail-updater in order to get a better understanding of how it works.
daemontools service setup
Set up the daemontools service directory and the logging:

Then set up the updater scripts:

We don't need to make any modifications to the update-qmail script as our program locations match those in the script already. So we can start the daemontools service:

After about 10 seconds, confirm that the service is running:

Want to test that the service is running? In one shell session, as root, watch the qmail-updater log file:

In another shell session, as a non-root user, send some date to the named pipe:

Set up the onchange script
Download the onchange script from John Simpson's website:

For a good test of the whole setup, watch the qmail-updater log::

Then, in another shell session, use vpopmail to add an email account:

The qmail-updater log should show that there were changes in the validrcptto.cdb file. The email account can be deleted:

Again, the log should show the change triggering qmail-updater.