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This filter implements the Rspamd protocol and allows OpenSMTPD to request an Rspamd analysis of an SMTP transaction before a message is committed to queue.


The filter currently supports:

  • greylisting
  • adding X-Spam related headers to a message
  • rewriting Subject
  • DKIM-signing message
  • Rspamd-provided SMTP replies
  • Allow Rspamd to add and remove headers


The filter is written in Golang and doesn't have any dependencies beyond the Go extended standard library.

It requires OpenSMTPD 6.6.0 or higher.

How to install

Install from your operating system's preferred package manager if available. On OpenBSD:

$ doas pkg_add opensmtpd-filter-rspamd
quirks-3.167 signed on 2019-08-11T14:18:58Z
opensmtpd-filter-rspamd-0.1.x: ok

Install using Go:

$ GO111MODULE=on go get
$ doas install -m 0555 ~/go/bin/filter-rspamd /usr/local/libexec/smtpd/filter-rspamd

Alternatively, clone the repository, build and install the filter:

$ cd filter-rspamd/
$ go build
$ doas install -m 0555 filter-rspamd /usr/local/libexec/smtpd/filter-rspamd

On Ubuntu the directory to install to is different:

$ sudo install -m 0555 filter-rspamd /usr/libexec/opensmtpd/filter-rspamd

How to configure

The filter itself requires no configuration.

It must be declared in smtpd.conf and attached to a listener for sessions to go through rspamd:

filter "rspamd" proc-exec "filter-rspamd"

listen on all filter "rspamd"

A remote rspamd instance can be specified by providing the -url parameter to the filter:

filter "rspamd" proc-exec "filter-rspamd -url"

listen on all filter "rspamd"

Optionally a -settings-id parameter can be used to select a specific rspamd setting. One usecase is for example to apply different rspamd rules to incoming and outgoing emails:

filter "rspamd-incoming" proc-exec "filter-rspamd"
filter "rspamd-outgoing" proc-exec "filter-rspamd -settings-id outgoing"

listen on all filter "rspamd-incoming"
listen on all port submission filter "rspamd-outgoing"

And in rspamd/local.d/settings.conf:

outgoing {
    id = "outgoing";
    apply {
        groups_enabled = ["dkim"];
        actions {
            reject = 100.0;
            greylist = 100.0;
            "add header" = 100.0;

Every email passed through the rspamd-outgoing filter will use the rspamd outgoing rule instead of the default rule.

Any configuration with regard to thresholds or enabled modules must be done in rspamd itself.