Mailbox cleaner with anti-spam filtering capabilities.

Track any changes to websites, and check for new email on multiple accounts. The program supports proxies, and it can be used as an email notification tool.

Program offering advanced filtering.

Switch between SMTP servers for all your application and email accounts. Program also enables other computers on your local network or the web to use your computer to send mail to an SMTP server.

Email filter. [Win]

An SMTP gateway for LAN combined with a filter facility to add/change/remove headers and x-headers.

Offers several free software tools, with source, and knowledge to provide everything one needs to migrate your email between systems.