D. J. Bernstein
Internet mail
Frequently asked questions


How many people use qmail?

Answer: As of October 2001, more than 700000 reachable IP addresses are running qmail as their SMTP server; qmail's growth over the past year is by far the fastest of any MTA. qmail handles a huge percentage of all Internet mail.

The qmail mailing list has more than 2000 subscribers (counting sublists as only one subscriber).

What are the most common reasons for using qmail?

Answer: Here are the top ten reasons I've heard from qmail users.

  1. Security. qmail doesn't let intruders into your machine.
  2. Reliability. qmail never loses mail.
  3. Speed. qmail delivers your mail much more quickly than sendmail, without compromising reliability.
  4. Low memory use. qmail can handle dozens of simultaneous deliveries on an old 16MB 486.
  5. User-controlled mailing lists. Users don't have to pester the system administrator to create new lists.
  6. Virtual hosts made easy. qmail pioneered multiple-domain support.
  7. Straightforward administration. qmail works with a minimum of fuss.
  8. Flexible program deliveries. qmail provides a powerful interface for external mail processors.
  9. Variable Envelope Return Paths. This feature (used by ezmlm) provides 100% automatic bounce handling for mailing lists of any size.
  10. The maildir format. This feature makes it easy to set up high-volume distributed POP toasters.

Is qmail compatible with sendmail?

Answer: Yes. qmail supports .forward, /etc/aliases, binmail deliveries to a central mail spool in the usual mbox format, the /usr/{lib,sbin}/sendmail interface for mail injection, and the normal UNIX user database in /etc/passwd. There is a checklist for large sites moving from sendmail to qmail.

What operating systems does qmail support?

Answer: qmail works on practically all UNIX systems: AIX, BSD/OS, FreeBSD, HP/UX, Irix, Linux, NetBSD, OpenBSD, OSF/1, SunOS, Solaris, etc. It automatically adapts itself to new UNIX variants.

qmail does not support Windows NT.

Is there really a cash reward for security holes?

Answer: Yes. See cr.yp.to/qmail/guarantee.html.