Code Quality Rank: L2
Programming language: C
License: GNU General Public License v3.0 or later
Tags: Mail Servers    
Latest version: v6.8.0.p1

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Version Coverity Scan analysis Packaging status License: ISC

OpenSMTPD is a FREE implementation of the server-side SMTP protocol as defined by RFC 5321 , with some additional standard extensions.

It allows ordinary machines to exchange e-mails with other systems speaking the SMTP protocol.

OpenSMTPD runs on various Unix and Unix-like operating systems including:

For more information: http://www.opensmtpd.org/portable.html

If you are looking for a comprehensive manual on how to build your own mail server visit our wiki.

Get In Touch

If you want to stay up to day with most recent developments or chat about OpenSMTPD you can:


The manual pages are available online, which you are encouraged to contribute to.

Install Via Package Manager

Many distributions already provide a packaged version of opensmtpd. All you need to do is install it via your package manager.

:warning: Some distributions might ship an old version of opensmtpd Be careful and check the version number to ensure you are running a secure version


sudo apt install opensmtpd


Has a dedicated wiki page

Alpine Linux

apk install opensmtpd


yum install opensmtpd


OpenSMTPD is available from MacPorts:

port install opensmtpd

Install From Source

Install Dependencies

OpenSMTPD relies on:

You will also need a C compiler and git if you are cloning the git repository

By default OpenSMTPD expects latest versions of all dependencies unless noted otherwise.

Note that some distributions have different packages for a same library, you should always use the -dev or -devel package (for example, libevent-dev or libevent-devel) if you're going to build OpenSMTPD yourself.

Get The Source Code

Clone from github:

git clone https://github.com/OpenSMTPD/OpenSMTPD.git

Download tarball

Latest release can always be found here


cd opensmtpd*
./bootstrap  # Only if you build from git sources
sudo make install
Special notes for FreeBSD/DragonFlyBSD/Mac OS X:

Please launch configure with special directive about libevent and libasr directory:

FreeBSD / DragonFlyBSD:
./configure --with-libasr=/usr/local
./configure --with-libevent=/opt/local

Though MacOS includes a copy of bison in the bases system, you will need to install a more recent version from, e.g., MacPorts.


sudo make install

Setup historical interface

OpenSMTPD provides a single utility smtpctl to control the daemon and the local submission subsystem.

To accomodate systems that require historical interfaces such as sendmail, newaliases or makemap, the smtpctl utility can operate in compatibility mode if called with the historical name.

On mailwrapper-enabled systems, this is achieved by editing /etc/mailer.conf and adding the following lines:

sendmail        /usr/sbin/smtpctl
send-mail       /usr/sbin/smtpctl
mailq           /usr/sbin/smtpctl
makemap         /usr/sbin/smtpctl
newaliases      /usr/sbin/smtpctl

Whereas on systems that don't provide mailwrapper, it can be achieved by setting the appropriate symbolic links:

ln -s /usr/sbin/smtpctl sendmail
ln -s /usr/sbin/smtpctl send-mail
ln -s /usr/sbin/smtpctl mailq
ln -s /usr/sbin/smtpctl makemap
ln -s /usr/sbin/smtpctl newaliases

The OpenSMTPD project leaves it up to the package maintainers to setup the links in their packages as it is very hard for us to accommodate all systems with the preferred method in a clean way.

Configure /etc/smtpd.conf

Please have a look at the complete format description of smtpd.conf configuration file

Add OpenSMTPD users

To operate, OpenSMTPD requires at least one user, by default _smtpd; and preferably two users, by default _smtpd and _smtpq.

Using two users instead of one will increase security by a large factor so... if you want to voluntarily reduce security or you have absolute more faith in our code than we do, by all means use one.

The instructions below assume the default users however, the configure script allows overriding these using the options: --with-user-smtpd, --with-user-queue, and --with-group-queue.

NetBSD, Linux (Debian, Arch Linux, ...)
mkdir /var/empty
useradd -c "SMTP Daemon" -d /var/empty -s /sbin/nologin _smtpd
useradd -c "SMTPD Queue" -d /var/empty -s /sbin/nologin _smtpq
DragonFlyBSD, FreeBSD
pw useradd _smtpd -c "SMTP Daemon" -d /var/empty -s /sbin/nologin
pw useradd _smtpq -c "SMTPD Queue" -d /var/empty -s /sbin/nologin
Mac OS X

First we need a group with an unused GID below 500, list the current ones used:

/usr/bin/dscl . -list /Groups PrimaryGroupID | sort -n -k2,2

Add a group - here we have picked 444:

/usr/bin/sudo /usr/bin/dscl . -create /Groups/_smtpd
PrimaryGroupID 444

Then the user. Again we need an unused UID below 500, list the current ones used:

/usr/bin/dscl . -list /Users UniqueID | sort -n -k2,2

Add a user - here we have picked 444:

/usr/bin/sudo /usr/bin/dscl . -create /Users/_smtpd UniqueID 444
/usr/bin/sudo /usr/bin/dscl . -delete /Users/_smtpd AuthenticationAuthority
/usr/bin/sudo /usr/bin/dscl . -delete /Users/_smtpd PasswordPolicyOptions
/usr/bin/sudo /usr/bin/dscl . -delete /Users/_smtpd dsAttrTypeNative:KerberosKeys
/usr/bin/sudo /usr/bin/dscl . -delete /Users/_smtpd dsAttrTypeNative:ShadowHashData
/usr/bin/sudo /usr/bin/dscl . -create /Users/_smtpd RealName "SMTP Daemon"
/usr/bin/sudo /usr/bin/dscl . -create /Users/_smtpd Password "*"
/usr/bin/sudo /usr/bin/dscl . -create /Users/_smtpd PrimaryGroupID 444
/usr/bin/sudo /usr/bin/dscl . -create /Users/_smtpd NFSHomeDirectory /var/empty
/usr/bin/sudo /usr/bin/dscl . -create /Users/_smtpd UserShell /usr/bin/false

repeat for the _smtpq user.

Launch smtpd

First, kill any running sendmail/exim/qmail/postfix or other.



or in debug and verbose mode

smtpd -dv

*Note that all licence references and agreements mentioned in the OpenSMTPD README section above are relevant to that project's source code only.