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Configuration

LSMTPD is configured using environment variables.

  • If you installed using apt install, a default config file is placed at: /etc/lsmtpd/lsmtpd.env. You can edit this file directly.

  • If you run LSMTPD from a binary or Docker, export the variables in your shell or pass them via --env options.

Server-Level Configuration​

These variables control how the LSMTPD server itself runs.

BIND_ADDRESS​

The IP address the SMTP server will bind to.

  • Use 0.0.0.0 to listen on all interfaces.
  • Use 127.0.0.1 to listen only locally.
BIND_ADDRESS=0.0.0.0

BIND_PORT​

The port the SMTP server listens on.

  • Default: 25 (standard SMTP).
  • If running as a non-root user, use a higher port (e.g. 2525).
BIND_PORT=25

SERVER_NAME​

Hostname used by the server for identification in logs and SMTP responses.

SERVER_NAME=mail.example.com

MAX_EMAIL_SIZE_BYTES​

Maximum allowed size of an incoming email, in bytes.

  • Default example below = 50 MB.
MAX_EMAIL_SIZE_BYTES=52428800

RUST_LOG​

To enable verbose logging for troubleshooting, you can set the RUST_LOG environment variable:

RUST_LOG=lsmtpd=TRACE
info

This uses the standard Rust logging format. You can adjust the log level (TRACE, DEBUG, INFO, WARN, ERROR) as needed.

AMQP-Level Configuration​

These variables define how LSMTPD connects to your AMQP broker (e.g., RabbitMQ).

danger

Ensure you have the correct AMQP broker settings before starting the server. If incorrect or connection fails, LSMTPD will save emails to the disk at /tmp/lsmtp for manual processing.

AMQP_HOST​

Hostname or IP address of the AMQP broker.

AMQP_HOST=rabbit.example.com

AMQP_PORT​

Port of the AMQP broker.

  • Default for AMQP: 5672.
  • Default for AMQP over TLS: 5671.
AMQP_PORT=5672

AMQP_USERNAME and AMQP_PASSWORD​

Credentials for authenticating with the AMQP broker.

AMQP_USERNAME=myuser
AMQP_PASSWORD=supersecret

AMQP_VHOST​

AMQP virtual host to use. If unsure, the default is usually /.

AMQP_VHOST=/

AMQP_EXCHANGE​

Name of the exchange where LSMTPD will publish messages.

AMQP_EXCHANGE=incoming_emails

AMQP_ROUTING_KEY​

Routing key to use when publishing messages. This determines which queue(s) receive the email.

AMQP_ROUTING_KEY=mail.events

AMQP_BUFFER_SIZE​

Maximum number of emails to buffer before sending to the AMQP broker.

  • Default: 100.
  • Increase if your broker is slow or if you expect bursty email traffic.
AMQP_BUFFER_SIZE=100

Example Configuration File​

Here’s an example /etc/lsmtpd/lsmtpd.env file with typical settings:

# LSMTPD Server Config
BIND_ADDRESS=0.0.0.0
BIND_PORT=25
SERVER_NAME=mail.example.com
MAX_EMAIL_SIZE_BYTES=52428800
RUST_LOG=lsmtpd=INFO

# AMQP Broker Config
AMQP_HOST=rabbit.example.com
AMQP_PORT=5672
AMQP_USERNAME=lsmtpd_user
AMQP_PASSWORD=supersecret
AMQP_VHOST=/
AMQP_EXCHANGE=incoming_emails
AMQP_ROUTING_KEY=mail.events
AMQP_BUFFER_SIZE=100
tip
  • Port Binding: If binding to port 25, LSMTPD may require root or CAP_NET_BIND_SERVICE.
  • Security: Store secrets (like AMQP_PASSWORD) in a secure location or a secrets manager.
  • Testing: Use telnet or swaks to verify that LSMTPD is listening on the expected address and port.