Postfix (Mail Transfer Agent)

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Basic data

developer IBM
Current  version 3.5.6
( July 26, 2020 )
operating system various Unix derivatives
programming language C.
category Mail Transfer Agent
License IBM Public License
German speaking No

Postfix is a mail transfer agent for Unix and Unix derivatives . At the time of development, the software should be a compatible alternative to Sendmail . The programmers paid particular attention to security aspects. The Postfix source code is available under the IBM Public License and is therefore free software .


Postfix was developed in 1998 by Wietse zweize Venema and initially published under the name VMailer. In the course of a trademark examination it was found that this name is very similar to another trademark and the name “ IBM Secure Mailer + Postfix” was given. Wietse Venema commented on the search for a name as follows:

We spent several months giving names to the program.

The IBM name policy killed every name we thought up, and so we
decided to change tactics. The program now has TWO names:
IBM Secure Mailer + Postfix.

The design goal was a fast, secure and easy to administer system.


Postfix is ​​a fast system that is easy to administer compared to Sendmail or qmail . Nevertheless, the following applies: Like any MTA, Postfix also requires in-depth knowledge of the mail server, protocols and extensive system knowledge, as the configurations can be very complex depending on the application.

Postfix placed particular emphasis on simple administration (since there are essentially only two configuration files) and a secure mail server. It is compatible with Sendmail, so it works with programs that would expect Sendmail as a mail server instead of Postfix. Furthermore, it has a modular structure and, as far as possible, executes its code without root rights. Configuration changes are possible during runtime and are adopted without restarting.

This modular structure is shown in the graphic below. There are four element types in this:

Yellow ellipses
They each stand for a daemon to which exactly one task has been assigned. This modularity explains the high level of security and stability that characterize Postfix.
Blue boxes
The blue boxes stand for so-called lookup tables (postfix maps) . They contain information in two columns that can be used for further processing of e-mails. This can be an access list that determines whether the e-mail is accepted or not, to rewrite the addressee or sender, or the further route (transport) an e-mail should take .
Yellow boxes
The yellow boxes stand for so-called queues, in which e-mails are physically stored on the data carrier (mostly hard disk or an NFS drive), or for final delivery, for example a user's mailbox (example: / var / mail / username).
White clouds
They stand for the possible entry or exit of the Postfix system. As an example on the left side the SMTP D daemon, which is responsible for accepting e-mails via TCP port 25 (unless otherwise configured). On the other hand, there is the SMTP Daemon, which is responsible for forwarding e-mails to other SMTPs.
Postfix architecture

All daemons (yellow ellipses) are started and monitored by the Postfix master process when required.

With version 3.0, SMTPUTF8, i.e. support for internationalized domain names and UTF-8 names in mailboxes and headers and dynamically linked libraries and database plug-ins, was added.

See also


Web links

Individual evidence

  1. Release 3.5.6 . July 26, 2020 (accessed July 27, 2020).
  2. ^ Gregor Longariva: Postfix - the Sendmail replacement? Modular and safe. In: Linux Magazin 05/2006. Retrieved January 26, 2010 .
  3. Mick Brauer and Brenno de Winter: Using Postfix for Secure SMTP Gateways. In: Retrieved on January 26, 2010 (English): "It's obvious that Mr. Venema has taken the lessons of history (as chronicled by CERT, bugtraq, et al.) Very much to heart."
  4. ^ Moritz Förster: Free Mail Transfer Agent Postfix 3.0 published. In: heise online . Heise Medien GmbH & Co. KG, February 10, 2015, accessed on July 19, 2019 .