postfixlimit

A lightweight, modern rate-limiting policy service for Postfix that protects you from outbound spam and runaway application mail.

Features

• Limits the number of messages sent through the Postfix MTA
• Supports multiple key types: client IP address, SASL authentication username, or sender address
• Flexible rate limit configuration with a global default — e.g. "100 messages per 2 hours"
• Pluggable storage backends: in-memory or Redis
• Three rate-limiting strategies: fixed-window, moving-window, and sliding-window

Installation

Quick Start

# install from pypi
PIPX_HOME=/opt/pipx PIPX_BIN_DIR=/usr/local/bin pipx install postfixlimit
# or installl from git repo directly
PIPX_HOME=/opt/pipx PIPX_BIN_DIR=/usr/local/bin pipx install git+https://github.com/yaroslaff/postfixlimit


wget https://raw.githubusercontent.com/yaroslaff/postfixlimit/refs/heads/master/contrib/postfixlimit.service
wget https://raw.githubusercontent.com/yaroslaff/postfixlimit/refs/heads/master/contrib/postfixlimit.conf

cp postfixlimit.service /etc/systemd/system/
systemctl daemon-reload

cp postfixlimit.conf /etc/

Once installed, edit /etc/postfixlimit.conf to configure field, default_limit, and any per-sender limits. Then start the daemon:

systemctl start postfixlimit

To cleanly uninstall:

PIPX_HOME=/opt/pipx PIPX_BIN_DIR=/usr/local/bin pipx uninstall postfixlimit

Systemd Unit File

Copy contrib/postfixlimit.service to /etc/systemd/system/postfixlimit.service, then reload and start the service:

systemctl daemon-reload
systemctl start postfixlimit

Configuration

An example configuration file is provided at contrib/postfixlimit.conf. Save it as /etc/postfixlimit.conf:

# Main server options
[server]
address = 127.0.0.1
port = 4455

# field is one of: sender / sasl_username / client_address
field = sender
default_limit = 5/day
action = DEFER
action_text = Limit ({limit}) exceeded for {field}={key}

# Storage backend: memory:// (default) or Redis
# storage = redis://localhost:6379/
storage = memory://

# Rate-limiting strategy: fixed-window / sliding-window / moving-window
strategy = fixed-window

dump_period = 60
dump_file = /var/lib/postfixlimit/limits.txt
log_file = /var/log/postfixlimit/postfixlimit.log

# Per-sender overrides
[limits]
aaa@example.com = 100 / day

Rate Limit Syntax

postfixlimit uses the limits library. Limits follow its string notation:

[count] [per|/] [n (optional)] [second|minute|hour|day|month|year]

Postfix Integration

Add the following to smtpd_recipient_restrictions in your Postfix main.cf:

smtpd_recipient_restrictions =
    check_policy_service inet:127.0.0.1:4455

Viewing Counter State

Every dump_period seconds, postfixlimit writes the current counter values to dump_file:

root@micromail:~# cat /var/lib/postfixlimit/limits.txt
Limits (2026-04-08 22:00:04):
  stg: 200 per 1 day remaining: 200
  odoomarketing: 1000 per 1 day remaining: 1000
  odoocare: 7000 per 1 day remaining: 6095
  mainweb: 3000 per 1 day remaining: 2991

Resetting Counters

Redis storage — reset a specific counter:

postfixlimit --reset COUNTERNAME

Reset all counters:

postfixlimit --reset ALL

In-memory storage — simply restart the daemon; all counters are cleared on startup.

Developer Reference

Postfix policy protocol specification: https://www.postfix.org/SMTPD_POLICY_README.html