spmfilter is a mail filtering framework. It attempts to be a general
filtering framework for any purpose. The API enables spmfilter plugins
to access messages as they are being processed by the MTA. This allows
them to examine and modify message content and meta-information during
the SMTP transaction. Plugins are loaded at runtime and can be processed
in any sequence. The processing chain can also be altered by a single
plugin, for example if the plugin has to stop further processing.
