libnewmail is a generic mail checking library for Unix/Linux
and other operating systems. It supports a simple API, an
extensible plugin architecture and asynchronous queries among
other features. Applications linking to libnewmail may enumerate
configured mailboxes, query mail box information and status and
request a mail spool auto-detection for users without any
libnewmail specific configuration. The library offers a clean
API to implement your own mail checking plugins.

WWW: http://0pointer.de/lennart/projects/libnewmail/