| 1 | qmail is a secure, reliable, efficient, simple message transfer agent. |
| 2 | It is meant as a replacement for the entire sendmail-binmail system on |
| 3 | typical Internet-connected UNIX hosts. |
| 4 | |
| 5 | Secure: Security isn't just a goal, but an absolute requirement. Mail |
| 6 | delivery is critical for users; it cannot be turned off, so it must be |
| 7 | completely secure. (This is why I started writing qmail: I was sick of |
| 8 | the security holes in sendmail and other MTAs.) |
| 9 | |
| 10 | Reliable: qmail's straight-paper-path philosophy guarantees that a |
| 11 | message, once accepted into the system, will never be lost. qmail also |
| 12 | supports maildir, a new, super-reliable user mailbox format. Maildirs, |
| 13 | unlike mbox files and mh folders, won't be corrupted if the system |
| 14 | crashes during delivery. Even better, not only can a user safely read |
| 15 | his mail over NFS, but any number of NFS clients can deliver mail to him |
| 16 | at the same time. |
| 17 | |
| 18 | Efficient: On a Pentium under BSD/OS, qmail can easily sustain 200000 |
| 19 | local messages per day---that's separate messages injected and delivered |
| 20 | to mailboxes in a real test! Although remote deliveries are inherently |
| 21 | limited by the slowness of DNS and SMTP, qmail overlaps 20 simultaneous |
| 22 | deliveries by default, so it zooms quickly through mailing lists. (This |
| 23 | is why I finished qmail: I had to get a big mailing list set up.) |
| 24 | |
| 25 | Simple: qmail is vastly smaller than any other Internet MTA. Some |
| 26 | reasons why: (1) Other MTAs have separate forwarding, aliasing, and |
| 27 | mailing list mechanisms. qmail has one simple forwarding mechanism that |
| 28 | lets users handle their own mailing lists. (2) Other MTAs offer a |
| 29 | spectrum of delivery modes, from fast+unsafe to slow+queued. qmail-send |
| 30 | is instantly triggered by new items in the queue, so the qmail system |
| 31 | has just one delivery mode: fast+queued. (3) Other MTAs include, in |
| 32 | effect, a specialized version of inetd that watches the load average. |
| 33 | qmail's design inherently limits the machine load, so qmail-smtpd can |
| 34 | safely run from your system's inetd. |
| 35 | |
| 36 | Replacement for sendmail: qmail supports host and user masquerading, |
| 37 | full host hiding, virtual domains, null clients, list-owner rewriting, |
| 38 | relay control, double-bounce recording, arbitrary RFC 822 address lists, |
| 39 | cross-host mailing list loop detection, per-recipient checkpointing, |
| 40 | downed host backoffs, independent message retry schedules, etc. In |
| 41 | short, it's up to speed on modern MTA features. qmail also includes a |
| 42 | drop-in ``sendmail'' wrapper so that it will be used transparently by |
| 43 | your current UAs. |