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I have Postfix setup on my server so that I can send outgoing mail using the command-line:

mail -s "Subject" address@example.com
  1. Is this using Sendmail or Postfix ?
  2. Is "Sendmail" just a software category or a distinct program ?
  3. If something is "Sendmail-ready" does that mean it will work with Postfix ?

Everything I've read online seems to use these two terms interchangeably.

Chaminda Bandara
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Xeoncross
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5 Answers5

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Postfix and sendmail are different implementations of Mail Transfer Agents which are using Simple Mail Transfer Protocol (SMTP) for email transport over the Internet.

Postfix first released in 1998 intended to be an alternative to the widely used Sendmail MTA which was used widely since 1982.

Here are the summaries of all 4 popular mail agents:

Postfix Summary Sendmail Summary

Exim Summary qmail Summary

And their comparison table:

MTA Suitability table

Source: shearer

For full comparison, check: MTA Comparison at shearer.org

kenorb
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Sendmail is a different (and much older) program from Postfix. However for every mail server to succeed in the Unix environment, a sendmail binary (with some of the expected command line options) must be provided.

EDIT: See for example the manual page for the sendmail program provided by Postfix

adamo
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    In another words, Postfix emulates Sendmail. – stepancheg Mar 07 '11 at 17:24
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    No it does not. It uses its own configuration files and does not understand sendmail.cf. – adamo Mar 07 '11 at 17:30
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    Postfix does emulate Sendmail's implementation of sendmail, the message submission program. Other than that, they serve the same purpose, but accomplish it by rather different means. – Phil Miller Mar 07 '11 at 17:45
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    Ok, so I can use most things that talk about requiring "sendmail" even though I have postfix setup because postfix has a mock-sendmail frontend script that handles everything. So my apps will never know it's not sendmail they are talking with. – Xeoncross Mar 07 '11 at 17:57
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Sendmail and Postfix are indeed both Mail Transfer Agents (MTAs).

Postfix is quite a bit easier for a new admin to set up, and has some nice features that integrate well with the mail store end of the process (Cyrus POP/IMAP, Dovecot, etc.).

If you're not actually going to be accepting email incoming into that box and it's getting forwarded to another system, something lighter such as Exim may be a better choice.

Magellan
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    I would love to setup Exim if it is noticeably smaller - but there just isn't that much out there on it unless you already know what your doing. – Xeoncross Mar 07 '11 at 23:03
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    We use Exim on the forwarding boxes because that's what Ubuntu installs by default with mailutils. Running dpkg-reconfigure exim4-config and 30 seconds of configuration work to point it at the mail server. – Magellan Mar 10 '11 at 17:48
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Architecture: The most common difference between these two is architecture. Postfix has a modular architecture composed of many independent small executables. It provides multiple options, parameters, and features. In contrast, Sendmail has a monolithic design that uses a single process always running at the backend.

Performance: Sendmail is not great in terms of its performance, making it a poor competitor. Postfix has a queue manager that handles the queuing much more quickly.

Source: https://linuxhint.com/postfix_vs_sendmail/

Avatar
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No, Postfix is definitively not the same thing as Sendmail.

In the context I just used, both refer to two different mail server software packages.

  1. /usr/bin/mail is very likely neither from Postfix nor Sendmail. With the command line options you mention, it will probably send an email with the help of /usr/sbin/sendmail. The latter is provided by your local Postfix for sending emails via the command line. – The name of that binary, though, was historically established by the Sendmail mail server software package, which was very dominant. (Unjustified, if you ask me.) That binary with some common command line arguments forms a de-facto standard for mail injection.

  2. “Sendmail” is not a software category. Written in upper case it very likely refers to the mail server software. Written in lower case it might also refer to the aforementioned binary, which is most often used to inject email(s) to the mail handling system (from whichever package that may be, including Postfix).

  3. “Sendmail-ready” sounds more like it works specifically with that Sendmail mail server software package. Nevertheless I would assume that it works with Postfix, or Postfix works with it. (Or that a more reasonable alternative exists which does work with Postfix.)

Robert Siemer
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