Binc IMAP is a GPL licensed IMAP4rev1 server for Maildir, written in C++.
It strives to be stable, fast, flexible, and RFC compliant.

For those familiar with qmail-pop3d, this IMAP server will be the natural
choice.  It is invoked similarly and uses checkpassword to authenticate.

WWW: https://sourceforge.net/projects/bincimap/