kumo.make_listener_domain {PARAMS}

Make a listener-domain configuration object.

The get_listener_domain event expects one of these to be returned to it (or a nil value).

A listener-domain contains information that affects whether an incoming SMTP message will be accepted and/or relayed.

By default, unless the client is connecting from one of the relay_hosts, relaying is denied.

PARAMS is a lua table that can accept the keys listed below.

relay_to

Optional boolean. Defaults to false. When set to true, allows relaying mail from anyone, so long as it is addressed to the requested domain.

kumo.on('get_listener_domain', function(domain, listener, conn_meta)
  if domain == 'example.com' then
    return kumo.make_listener_domain {
      relay_to = true,
    }
  end
end)

Enable relaying based on SMTP authentication

This example shows how to use the connection metadata information to determine if the current session is authenticated, and use that to govern whether relaying is allowed.

In this example, any user is permitted to relay to anywhere:

kumo.on('get_listener_domain', function(domain, listener, conn_meta)
  if conn_meta:get_meta 'authz_id' then
    -- We're authenticated as someone.
    -- Allow relaying
    return kumo.make_listener_domain {
      relay_to = true,
    }
  end
end)

A more sophisticated configuration might use a mapping to control which domains are allowed relaying based on the authorization id:

local RELAY_BY_DOMAIN = {
  ['example.com'] = {
    -- The user scott is permitted to relay to example.com
    ['scott'] = true,
  },
}

kumo.on('get_listener_domain', function(domain, listener, conn_meta)
  local dom_map = RELAY_BY_DOMAIN[domain]
  if dom_map then
    local authz_id = conn_meta:get_meta 'authz_id'
    if dom_map[authz_id] then
      return kumo.make_listener_domain {
        relay_to = true,
      }
    end
  end
end)

log_oob

Optional boolean. Defaults to false. When set to true, if the incoming mail is an out-of-band (OOB) bounce report formatted according to RFC 3464, and is addressed to the requested domain, the message will be accepted and logged to the delivery logs.

kumo.on('get_listener_domain', function(domain, listener, conn_meta)
  if domain == 'bounce.example.com' then
    return kumo.make_listener_domain {
      log_oob = true,
    }
  end
end)

log_arf

Optional boolean. Defaults to false. When set to true, if the incoming mail is an ARF feedback report formatted according to RFC 5965, and is addressed to the requested domain, the message will be accepted and logged to the delivery logs.

kumo.on('get_listener_domain', function(domain, listener, conn_meta)
  if domain == 'fbl.example.com' then
    return kumo.make_listener_domain {
      log_arf = true,
    }
  end
end)

relay_from

Optional CIDR list. Defaults to an empty list. If the connected client is from an IP address that matches the CIDR list, and the sending domain matches the requested domain, then relaying will be allowed.

kumo.on('get_listener_domain', function(domain, listener, conn_meta)
  if domain == 'send.example.com' then
    return kumo.make_listener_domain {
      relay_from = { '10.0.0.0/24' },
    }
  end
end)