About Logging Message Headers

KumoMTA Policy
1

Ref KumoMTA doc:

Our recommendation is to capture the headers into the message metadata to make the system run faster and more efficiently:
kumo.on('init', function()
  kumo.configure_local_logs {
    -- ..
    meta = { 'subject', 'x_client_id' },
  }
end)

kumo.on('smtp_server_message_received', function(msg, conn_meta)
  -- Arrange to log the subject header in the most
  -- efficient way, by capturing it into the message
  -- metadata when we receive the message.
  -- The `msg:import_x_headers` method will capture non-x-header
  -- names when header names are explicitly passed like this:
  msg:import_x_headers { 'subject', 'x-client-id' }
end)

But when i test , after msg:import_x_headers should add some code:

msg:set_meta('Subject', msg:get_first_named_header_value 'Subject')

If so, is it better to write it in the document? Or is he self-evident

3

Import_X_Headers is already moving your headers into the metadata, but as per the name it is only importing X headers. Subject is not an X header.

4

Thanks Mike.
Subject it is, but I also tested the X-Tenant and X-Campaign fields. When there is no msg:set_meta, it cannot be obtained. The detailed configuration is as follows:

kumo.on('smtp_server_message_received', function(msg)
  -- Protect against SMTP Smuggling (https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/)
  local failed = msg:check_fix_conformance(
    -- check for and reject messages with these issues:
    'NON_CANONICAL_LINE_ENDINGS',
    -- fix messages with these issues:
    ''
  )
  if failed then
    kumo.reject(552, string.format('5.6.0 %s', failed))
  end
  msg:import_x_headers { 'from','Subject','X-Smtp-API','X-System', 'Message-Id' ,'X-Tenant','X-Campaign' }
 
  -- Call the queue helper to set up the queue for the message.
  msg:set_meta('from', msg:get_first_named_header_value 'from')
  msg:set_meta('Subject', msg:get_first_named_header_value 'Subject')
  msg:set_meta('Message-Id', msg:get_first_named_header_value 'Message-Id')

webhook(elk)

log_hooks:new {
  name = 'elk',
  batch_size = 500,

  -- log_parameters are combined with the name and
  -- passed through to kumo.configure_log_hook
  log_parameters = {
    -- metadata extracted from headers in smtp_server_message_received
    meta = { 'from', 'Subject' ,'X-Smtp-API','X-System','Message-Id','X-Tenant','X-Campaign' },
    per_record = {
      Any = { enable = true },
    },
  },

  constructor = function(domain, tenant, campaign)
    -- send elk code
  end,
}

After this config only from ,Subject,Message-Id can pass data to elk.

5

When you use the import function, variable names are normalized to lowercase and dashes become underscores. So X-My-Header will be saved as meta variable x_my_header.
If you test for meta X-My-Header it will be nil

6

Ohhhh, Thanks Tom.