Qmail is a secure, reliable, efficient, simple
message transfer agent. It is meant to be a replacement for the entire sendmail-binmail
system on typical Internet-connected UNIX hosts.
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.
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.
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.
qmail is vastly smaller than any other Internet MTA. Some reasons
(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.
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.
more information on : www.qmail.org