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Programming language: C
Tags: Email     Communication systems     Mail Transfer Agents    
Latest version: v6.7.1.p1

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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 top of the OpenBSD operating system but also has a portable version that can build and run on several systems, including:

  • Linux
  • FreeBSD
  • NetBSD
  • DragonFly

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

People interested about OpenSMTPD are encouraged to subscribe to our mailing list: http://www.opensmtpd.org/list.html

and to join the IRC channel: #OpenSMTPD @ irc.freenode.net

Also note that we have a wiki at https://github.com/OpenSMTPD/OpenSMTPD/wiki that you are encouraged to contribute to.


How to build, configure and use Portable OpenSMTPD


Portable OpenSMTPD relies on:

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

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


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

Mac OS X:

./configure --with-libevent=/opt/local --with-libasr=/opt/local


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 accomodate all systems with the prefered method in a clean way.

Configure /etc/smtpd.conf

Please have a look at the complete format description of smtpd.conf configuration file (https://man.openbsd.org/smtpd.conf)

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.