On Dynamically Typed today, there's this new post about "Inbound mail with PHP and vpopmail".

I suspect many of you - like SitePoint - use PHP to process inbound email for various purposes. I've hit problems in the past trying to shoehorn this behavior into our vpopmail installation. Vpopmail is a handy set of patches for qmail that ease the handling of large numbers of email domains and users.

The key problem is, vpopmail generally runs as the "vpopmail" user, and delivers all mail while executing under this UID. I discovered that our best bet was to create a local domain to have the relevant emails delivered to.

With the addition of a local domain to deliver the mail to, the scripts running on incoming mail can be assigned back into the user's realm (rather than the user running vpopmail) and let them execute once again as that "someuser".