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- qmail is a secure, reliable, efficient, simple message transfer agent.
- It is meant as a replacement for the entire sendmail-binmail system on
- typical Internet-connected UNIX hosts.
-
- Secure: Security isn't just a goal, but an absolute requirement. Mail
- delivery is critical for users; it cannot be turned off, so it must be
- completely secure. (This is why I started writing qmail: I was sick of
- the security holes in sendmail and other MTAs.)
-
- Reliable: qmail's straight-paper-path philosophy guarantees that a
- message, once accepted into the system, will never be lost. qmail also
- supports maildir, a new, super-reliable user mailbox format. Maildirs,
- unlike mbox files and mh folders, won't be corrupted if the system
- crashes during delivery. Even better, not only can a user safely read
- his mail over NFS, but any number of NFS clients can deliver mail to him
- at the same time.
-
- Efficient: On a Pentium under BSD/OS, qmail can easily sustain 200000
- local messages per day---that's separate messages injected and delivered
- to mailboxes in a real test! Although remote deliveries are inherently
- limited by the slowness of DNS and SMTP, qmail overlaps 20 simultaneous
- deliveries by default, so it zooms quickly through mailing lists. (This
- is why I finished qmail: I had to get a big mailing list set up.)
-
- Simple: qmail is vastly smaller than any other Internet MTA. Some
- reasons why: (1) Other MTAs have separate forwarding, aliasing, and
- mailing list mechanisms. qmail has one simple forwarding mechanism that
- lets users handle their own mailing lists. (2) Other MTAs offer a
- spectrum of delivery modes, from fast+unsafe to slow+queued. qmail-send
- is instantly triggered by new items in the queue, so the qmail system
- has just one delivery mode: fast+queued. (3) Other MTAs include, in
- effect, a specialized version of inetd that watches the load average.
- qmail's design inherently limits the machine load, so qmail-smtpd can
- safely run from your system's inetd.
-
- Replacement for sendmail: qmail supports 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, etc. In
- short, it's up to speed on modern MTA features. qmail also includes a
- drop-in ``sendmail'' wrapper so that it will be used transparently by
- your current UAs.
-