netqmail

Secure, reliable, efficient, simple, and fast MTA

The qmail program is a secure, reliable, efficient simple message transfer agent. It is meant to be a replacement for the entire sendmail-binmail system that most UNIX hosts use. Although qmail holds security and reliability as its top two priorities, it is also fast. On a Pentium under BSD/OS, qmail can easily handle 200000 separate messages per day that are injected and must then be delivered to local mailboxes! Security and reliability are qmail's two strengths, however. The qmail package ensures a message, once accepted, will never be lost. An optional new mailbox format, maildir, even lets users safely read their mail over NFS, while still accepting new mail deliveries. The following features are supported: host and user masquerading, full host hiding, virtual domains, null clients, list-owner rewriting, relay control, double-bounce recording, arbitrary RFC 822 address lists, cross-host mailing-list loop detection, per-recipient checkpointing, downed host backoffs, independent message retry schedules, a drop-in sendmail replacement, and more! http://pobox.com/~djb/qmail.html