popa3d is a tiny POP3 daemon for Unix-like operating systems. It was designed with security as the primary goal.
popa3d has been integrated into OpenBSD base tree. It is the default POP3 server on Openwall GNU/*/Linux (Owl), recent versions of Slackware, and distributions by ALT Linux team. popa3d is also a part of Debian GNU/Linux, Gentoo Linux, and ASPLinux.