Linux installation

The installation described above was performed on an Ubuntu Server 20.04. There may be slight changes to apply for other distributions.

Install Rust language

If you want to install Rust in the most straightforward, recommended way, then use Rustup and follow the instructions.

curl --proto '=https' --tlsv1.2 -sSf | sh

Check dependencies

vSMTP requires libc libraries and GCC compiler/linker. On a Debian system these can be installed through the build-essential package.

sudo apt install pkg-config
sudo apt install build-essential

The Transport Layer Security protocol (TLS) is provided by OpenSSL development libraries. The Debian package is libssl-dev package.

sudo apt install libssl-dev

The authentication is provided by the GNU gsasl and Cyrus sasl libraries.

sudo apt install libgsasl7-dev
sudo apt install libsasl2-2
sudo apt install sasl2-bin

Libclang frontend is also required.

sudo apt install libclang-dev

vSMTP compilation

Cargo (Rust package manager) will download all required dependencies and compile the source code in accordance with your environment.

$ git clone -b main
$ cargo build --release --workspace
$ ./target/release/vsmtp --help
vsmtp 1.0.0
Team viridIT <>
Next-gen MTA. Secured, Faster and Greener


    -c, --config <CONFIG>      Path of the vSMTP configuration file (toml format)
    -h, --help                 Print help information
    -n, --no-daemon            Do not run the program as a daemon
    -t, --timeout <TIMEOUT>    Make the server stop after a delay (human readable format)
    -V, --version              Print version information

    config-diff    Show the difference between the loaded config and the default one
    config-show    Show the loaded config (as serialized json format)
    help           Print this message or the help of the given subcommand(s)

By default Rust/Cargo use static linking to compile - all libraries required are compiled into the executable - allowing vSMTP to be a standalone application.

Configure the Operating System for vSMTP

For security purpose, vSMTP should run using a dedicated account with minimal privileges.

$ sudo adduser --system --shell /usr/sbin/nologin --no-create-home \
    --uid 9999 --group --disabled-password --disabled-login vsmtp
Adding system user 'vsmtp' (UID 9999) ...
Adding new group 'vsmtp' (GID 9999) ...
Adding new user 'vsmtp' (UID 9999) with group 'vsmtp' ...
Not creating home directory '/home/vsmtp'.

vSMTP binaries and config files should be located in:

  • /usr/sbin/ for binaries
  • /etc/vsmtp/
    • /etc/vsmtp/vsmtp.toml : the default configuration file
    • /etc/vsmtp/rules/ for rules
    • /etc/vsmtp/certs/ for certificates
  • /var/spool/vsmtp/ for internal queues
  • /var/log/
    • /var/log/vsmtp/ for internal logs and trace
    • /var/log/mail.log and mail.err for syslog (not implemented in current release)
  • /home/~user/Maildir for local IMAP delivery

This default behavior can be changed in the vSMTP configuration file /etc/vsmtp/vsmtp.toml which is called at startup by the vsmtp service script.

$ sudo mkdir /etc/vsmtp /etc/vsmtp/rules /etc/vsmtp/certs /var/log/vsmtp /var/spool/vsmtp
$ sudo cp ./target/release/vsmtp /usr/sbin/
$ sudo cp ./target/release/vqueue /usr/sbin/

Create a minimal vsmtp.toml configuration file that matches vsmtp version (i.e. 1.0.0)

$ sudo bash -c 'echo "version_requirement = \">=1.0.0\"" > /etc/vsmtp/vsmtp.toml'

Grant rights to files and folders.

$ sudo chown -R vsmtp:vsmtp /var/log/vsmtp /etc/vsmtp/* /var/spool/vsmtp

If required, do not forget to add your private key and certificate to /etc/vsmtp/certs and allow vsmtp user to read them.

Configuring the MTA service

Check and disable current MTA

Check if you have a mail transfer agent service running and disable it. The example below is related to a Postfix service running on port 25.

$ sudo ss -ltpn | grep ":25"
tcp        0      0    *               LISTEN      39423/master
$ sudo systemctl status postfix
● postfix.service - Postfix Mail Transport Agent
     Loaded: loaded (/lib/systemd/system/postfix.service; enabled; vendor preset: enabled)
     Active: active (exited) since Fri 2021-12-10 11:10:58 CET; 5min ago
    Process: 39426 ExecStart=/bin/true (code=exited, status=0/SUCCESS)
   Main PID: 39426 (code=exited, status=0/SUCCESS)
$ sudo systemctl stop postfix
$ sudo systemctl disable postfix
Synchronizing state of postfix.service with SysV service script with /lib/systemd/systemd-sysv-install.
Executing: /lib/systemd/systemd-sysv-install disable postfix
Removed /etc/systemd/system/

☞ | Depending on Linux distributions, instead of ss command you may have to use netstat -ltpn

Add vSMTP as a systemd service

Copy the daemon configuration file to /etc/systemd/system.

$ sudo cp ./tools/install/deb/vsmtp.service /etc/systemd/system/vsmtp.service

Please note that vSMTP comes with a mechanism that drop privileges at startup. The service type must be set to forking.

Do not modify this file unless you know what you are doing.

Enable and activate vSMTP service

$ sudo systemctl enable vsmtp.service
Created symlink /etc/systemd/system/ → /etc/systemd/system/vsmtp.service.

$ sudo systemctl start vsmtp

$ sudo systemctl status vsmtp
● vsmtp.service - vSMTP Mail Transfer Agent
     Loaded: loaded (/etc/systemd/system/vsmtp.service; enabled; vendor preset: enabled)
     Active: active (running) since Fri 2021-12-10 11:32:15 CET; 21s ago
   Main PID: 2164 (vsmtp)
      Tasks: 25 (limit: 38287)
     Memory: 39.9M
     CGroup: /system.slice/vsmtp.service
             └─2164 /usr/sbin/vsmtp -c /etc/vsmtp/vsmtp.toml

Check that vSMTP is working properly

$ ss -ltpn | grep vsmtp
State    Recv-Q   Send-Q     Local Address:Port     Peer Address:Port   Process
LISTEN   0        128 *       users:(("vsmtp",pid=2127,fd=5))
LISTEN   0        128 *       users:(("vsmtp",pid=2127,fd=6))
LISTEN   0        128  *       users:(("vsmtp",pid=2127,fd=4))

$ nc -C localhost 25
220 Service ready
451 Timeout - closing connection.