postfix-ratelimiter

A simple policy daemon which rate-limits sending mails based on sasl_username. Recipient count is rate-limited.

Quick deployment in Kubernetes

Check out examples.

Postfix configuration

A sample postfix configuration might look like:

smtpd_data_restrictions = ...
    check_policy_service { inet:postfix-ratelimiter:10028, { default_action=dunno } },
    permit

Legacy/standalone usage

$ ./postfix-ratelimiter -h
Usage of ./postfix-ratelimiter:
  -dbdriver="": Database type for dynamic rate/burst lookups (mysql or postgresql)
  -dbdsn="": Database DSN for dynamic rate/burst lookup
  -default-burst=60: Default burst for policing
  -default-rate=1: Default rate for policing (recipient/seconds)
  -policy-listen-address=":10028": Postfix Policy listen address
  -querystring="": SQL Query returning dynamic (rate, burst) settings for a (local_part, domain) lookup
  -web-listen-address=":9026": Exporter WEB listen address

The policy daemon will create a token-bucket rate-limiter for each sasl authenticated user. Rate-limits against unauthenticated mails are not enforced. The token-buckets will have default-rate rate and default-burst burst settings.

By default the daemon listens on :10028 for policy requests.

Statistics

Rejected recipient count is export in Prometheus format:

$ curl -s http://127.0.0.1:9026/metrics | grep postfix_ratelimiter_rejects
# HELP postfix_ratelimiter_rejects Rejected recipient count
# TYPE postfix_ratelimiter_rejects counter
postfix_ratelimiter_rejects{sasl_username="[email protected]"} 8

Dynamic rate/burst

You can specify a database to look up rate/burst settings dynamically.

For this, you'll have to specify -dbdriver (mysql or postgres), the DSN the driver uses (mysql or postgres), and the -querystring which must return one row with two columns: (rate, burst). The querystring is prepared, and during lookup, (local_part, domain) is passed as an argument.

Null returned for any of the columns is treated as Infinity.

Example with postgresql, minimal schema:

create table rate_limits (
    local_part varchar(128),
    domain varchar(128),
    rate float,
    burst float,
    primary key (local_part, domain)
);

$ ./postfix-ratelimiter -dbdriver=postgres -dbdsn "postgres://localhost?sslmode=disable" -querystring='select rate, burst from rate_limits where local_part = $1 and domain = $2'

Containerized deployment

Configuration arguments are parsed using flag, so they can be specified using capitalized environment variables too. For example, you can start the app as:

$ docker run -d --restart=always -p 10028:10028 -e DEFAULT_RATE=2 -e DEFAULT_BURST=100 ghcr.io/rkojedzinszky/postfix-ratelimiter