mailcow/data/conf/rspamd/local.d/dkim.conf

sign_condition =<<EOD
return function(task)
  local smtp_from = task:get_from('smtp')
  local mime_from = task:get_from('mime')
  local rspamd_logger = require "rspamd_logger"
  if smtp_from[1]['domain'] ~= nil and smtp_from[1]['domain'] ~= '' then
    domain = smtp_from[1]['domain']
    rspamd_logger.infox(task, "set domain found in smtp from field to %s", domain)
    if not task:get_user() then
      rspamd_logger.infox(task, "found domain in smtp header field, but user is not authenticated - skipped")
      return false
    end
  elseif mime_from[1]['domain'] ~= nil and mime_from[1]['domain'] ~= '' then
    domain = mime_from[1]['domain']
    rspamd_logger.infox(task, "set domain found in mime from field to %s", domain)
  else
    rspamd_logger.infox(task, "cannot determine domain for dkim signing")
    return false
  end
  local keyfile = io.open("/data/dkim/keys/" .. domain .. ".dkim")
  if keyfile then
    rspamd_logger.infox(task, "found dkim key file for domain %s", domain)
    keyfile:close()
    return {
      key = "/data/dkim/keys/" .. domain .. ".dkim",
      domain = domain,
      selector = "dkim"
    }
  else
    rspamd_logger.infox(task, "no key file for domain %s - skipped", domain)
  end
  return false
end
EOD;