The OpenSMTPD server seeks to be {
*} as secure as possible, and uses privilege separation to mitigate {
} possible security bugs {
*} as reliable as possible: any accepted email must not be lost {
*} lean: it covers typical usage cases instead of every obscure one {
*} easy to configure, with a configuration syntax reminiscent of the OpenBSD {
} Packet Filter's (PF) {
*} fast and efficient: it can handle large queues with reasonable performance

WWW: https://www.opensmtpd.org
