Introduction Introduction Courier is a modular multiprotocol mail server that's designed to strike a balance between reasonable performance, flexibility and features. Features Can be configured to function as an intermediate mail relay, or as a mail server that receives mail for one or more domains, or anything in between. Uses the maildir format as its native mail storage format.
Some support is provided for legacy mbox mailboxes.
This is pretty much the highest level of security that can be achieved with today's technologies. This doesn't even require DNSsec. This work is mostly complete, but still needs a little testing. Mailboxes can be accessed via POP3. Courier source distribution includes an integrated POP3 server.