This » PECL extension is not bundled with PHP. Information for installing this PECL extension may be found in the manual chapter titled Installation of PECL extensions. Additional information such as new releases, downloads, source files, maintainer information, and a CHANGELOG, can be located here: » http://pecl.php.net/package/mailparse.
In order to use these functions you must compile PHP with mailparse support by using the --enable-mailparse configure option.
Windows users will enable php_mailparse.dll inside of php.ini in order to use these functions. A DLL for this PECL extension is currently unavailable. See also the building on Windows section.