There is a more robust version of this extension, and other goodies for working with vpopmail from PHP available at: http://pmailadmin.sourceforge.net/
The extension will get added back to PECL once it is finished and tested.
CLI. vpopmail Functions
This extension has been moved from PHP as of PHP 4.3.0 and now vpopmail lives in PECL.
As of PHP 4, these functions are only available if PHP was configured with --with-vpopmail[=DIR].
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