qmail – modern SMTP server

qmail is an Internet Mail Transfer Agent (MTA). It was written as a more secure replacement for the popular Sendmail program.

qmail uses the Simple Mail Transfer Protocol (SMTP) to exchange messages with MTA’s on other systems.

The software is released under an open source license.

Features include:

  • Secure:
    • Clear separation between addresses, files, and programs.
    • Minimization of setuid code.
    • Minimization of root code.
    • Five-way trust partitioning–security in depth.
    • Optional logging of one-way message hashes, entire message contents, etc.
  • Message construction:
    • RFC 822 and RFC 1123 compliant.
    • Full support for address groups.
    • Automatic conversion of old-style address lists to RFC 822 format
      sendmail command for compatibility with current user agents.
    • Header line length limited only by memory.
    • Host masquerading.
    • User masquerading.
    • Automatic Mail-Followup-To creation.
  • SMTP service:
    • RFC 821, RFC 1123, RFC 1651, RFC 1652, and RFC 1854 compliant 8-bit clean.
    • RFC 931/1413/ident/TAP callback–can help track spammers/forgers.
    • Relay control–stops unauthorized relaying by outsiders.
    • No interference between relay control and aliases.
    • Automatic recognition of local IP addresses.
    • Per-buffer timeouts.
    • Hop counting.
    • Parallelism limit (via ucspi-tcp).
    • Refusal of connections from known abusers (via ucspi-tcp).
    • Relaying and message rewriting for authorized clients.
    • Optional RBL/ORBS support (via rblsmtpd).
  • Reliable.
  • Efficient – performing up to 20 deliveries simultaneously, by default.
  • Queue management:
    • Instant handling of messages added to queue.
    • Parallelism limits.
    • Split queue directory–no slowdown when queue gets big.
    • Quadratic retry schedule–old messages tried less often.
    • Independent message retry schedules.
    • Automatic safe queueing–no loss of mail if system crashes.
    • Automatic per-recipient checkpointing.
    • Automatic queue cleanups.
    • Queue viewing.
    • Detailed delivery statistics (via qmailanalog).
  • Bounces:
    • QSBMF bounce messages–both machine-readable and human-readable.
    • HCMSSC support–language-independent RFC 1893 error codes.
    • Double bounces sent to postmaster.
  • Routing by domain:
    • Any number of names for local host.
    • Any number of virtual domains.
    • Domain wildcards.
    • Configurable “percent hack” support.
    • UUCP hook.
  • SMTP delivery:
    • RFC 821, RFC 974, and RFC 1123 compliant.
    • 8-bit clean.
    • Automatic downed host backoffs.
    • Artificial routing–smarthost, localnet, mailertable.
    • per-buffer timeouts.
    • Passive SMTP queue–perfect for SLIP/PPP.
    • AutoTURN support (via serialmail).
  • Forwarding and mailing lists:
    • Sendmail .forward compatibility (via dot-forward).
    • Hashed forwarding databases (via fastforward).
    • Sendmail /etc/aliases compatibility (via fastforward).
    • Address wildcards.
    • Mailing list owners–automatically divert bounces and vacation messages.
    • VERPs–automatic recipient identification for mailing list bounces.
    • Delivered-To–automatic loop prevention, even across hosts.
  • Local delivery:
    • User-controlled address hierarchy–fred controls fred-anything mbox delivery.
    • Reliable NFS delivery.
    • User-controlled program delivery: procmail etc.
    • Optional new-mail notification.
    • Optional NRUDT return receipts.
    • Conditional filtering.
  • POP3 service:
    • RFC 1939 compliant.
    • UIDL support.
    • TOP support.
    • APOP hook.
    • modular password checking (via checkpassword).

Support: FAQ
Developer: Open Systems AG
License: GNU General Public License v2.0

qmail is written in C. Learn C with our recommended free books and free tutorials.

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