While wading through one of my buildouts, it occurred to me that I should look up the documentation for Plone's PrintingMailHost. This product is very nice for a developer, and I have been using it for some time. But today, I actually read the documentation and found this warning, which so far had escaped me:

If Zope is not running in debug mode, it will not install itself. However, I wouldn't recommend putting it on a production site. You never know what those monkeys may get up to...

I wanted the PrintingMailHost only in my development instance, and therefore changed my setup a little. Instead of globally adding the product to my eggs listing, I added it only for the development buildout:

[secondary]
... copy from the main buildout, then:

eggs =
    ${buildout:eggs}
    Products.PrintingMailHost

After re-running buildout, none of my production instances had a PrintingMailHost anymore.

Enjoy!