spmfilter邮件过滤框架

spmfilter 是一个邮件过滤框架，其目标是成为一个通用的满足各种过滤要求的框架。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.