rule.lua

rspamd_config.R_EMPTY_IMAGE = {
    callback = function(task)
      local tp = task:get_text_parts() -- get text parts in a message
      
      for _,p in ipairs(tp) do -- iterate over text parts array using `ipairs`
        if p:is_html() then -- if the current part is html part
          local hc = p:get_html() -- we get HTML context
          local len = p:get_length() -- and part's length
          
          if len < 50 then -- if we have a part that has less than 50 bytes of text
            local images = hc:get_images() -- then we check for HTML images
            
            if images then -- if there are images
              for _,i in ipairs(images) do -- then iterate over images in the part
                if i['height'] + i['width'] >= 400 then -- if we have a large image
                  return true -- add symbol
                end
              end
            end
          end
        end
      end
    end,
    score = 3.0, -- default score
    condition = function(task) -- condition for the rule
        if task:get_header('Subject') then
            return true
        end
        return false
    end,
    description = 'No text parts and a large image',
}

-- Regular expression rule example
config['regexp']['RE_TEST'] = {
    re = '/test/P',
    score = 2.0,
    condition = function(task)
        if task:get_header('Subject') then
            return true
        end
        return false
    end,
}