Commit | Line | Data |
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2117e02e MW |
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. |