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:
- Linux
- FreeBSD
- OpenBSD
- NetBSD
- DragonFlyBSD
- OSX
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.
If you want to stay up to day with most recent developments or chat about OpenSMTPD you can:
- subscribe to our mailing list: http://www.opensmtpd.org/list.html
- join the IRC channel:
#opensmtpd@ irc.libera.chat - submit a bug report or a feature request here on GitHub
- visit GitHub's discussions page
The manual pages are available online, which you are encouraged to contribute to.
Many distributions already provide a packaged version of opensmtpd. All you need to do is install it via your package manager.
⚠️ 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
apk install opensmtpd
yum install opensmtpd
OpenSMTPD is available from MacPorts:
port install opensmtpd
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.
Clone from github:
git clone https://github.com/OpenSMTPD/OpenSMTPD.git
Latest release can always be found here
cd opensmtpd*
./bootstrap # Only if you build from git sources
./configure
make
sudo make install
Please launch configure with special directive about libevent and libasr directory:
./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
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.
Please have a look at the complete format description of smtpd.conf
configuration file
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.
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
pw useradd _smtpd -c "SMTP Daemon" -d /var/empty -s /sbin/nologin
pw useradd _smtpq -c "SMTPD Queue" -d /var/empty -s /sbin/nologin
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.
First, kill any running sendmail/exim/qmail/postfix or other.
Then:
smtpd
or in debug and verbose mode
smtpd -dv