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Common Questions

Here are some common questions and answers about LSMTPD.

❓ What is LSMTPD?​

LSMTPD (Lightweight SMTP Daemon) is a minimal SMTP server written in Rust.
It receives email over SMTP and forwards it directly into an AMQP queue or exchange.

❓ Why should I use LSMTPD instead of Postfix or Exim?​

Traditional MTAs (Postfix, Exim, Sendmail) are powerful but heavy.
If all you need is “receive an email → push it into AMQP”, LSMTPD is:

  • Lighter.
  • Easier to configure.
  • More predictable in containerized or microservice environments.

Use Postfix/Exim if you need advanced features (mail storage, outbound relay, spam filtering).

❓ Can LSMTPD send outbound mail?​

No. LSMTPD is receive-only.
It is intentionally designed for one purpose: ingesting mail and forwarding it to AMQP.

❓ What AMQP brokers are supported?​

Any broker that implements AMQP 0.9.1 or AMQP 1.0 should work.

  • ✅ Tested with RabbitMQ.
  • ✅ Likely works with Apache Qpid and others.

❓ How do I configure LSMTPD?​

Configuration is done via environment variables (or /etc/lsmtpd/lsmtpd.env on Debian installs).
See the Configuration Guide for details.

❓ What ports does LSMTPD use?​

  • Default SMTP: 25 (or 2525 if running unprivileged).
  • AMQP: 5672 (default) or 5671 (TLS).

❓ How do I verify LSMTPD is running?​

You can test with:

telnet localhost 25

or using swaks:

swaks --server localhost --helo test --from test@example.com --to inbox@example.com

❓ What license is LSMTPD under?​

LSMTPD is licensed under GPL-3.0. You are free to use, inspect, and contribute.

👉 Source code: github.com/Neko-Nik/LSMTP

❓ Who maintains LSMTPD?​

LSMTPD is developed and maintained by Neko Nik.