kumomta/docs/reference/events/smtp_server_message_received.md

kumo.on('smtp_server_message_received', function(message))

Called by the ESMTP server after receiving the message data.

If the client issued multiple "RCPT TO" commands in the same transaction, each one will result in a separate message being created, and this event will be triggered for each of them.

The event handler will be passed a Message object. The Message will always have a Received header prepended that captures trace information about the sender.

This event is the best place to carry out a number of important policy decisions:

• DKIM signing via message:dkim_sign.
• Assigning the "campaign", "tenant" and/or "queue" meta values via msg:set_meta

-- Called once the body has been received.
-- For multi-recipient mail, this is called for each recipient.
kumo.on('smtp_server_message_received', function(msg)
  local signer = kumo.dkim.rsa_sha256_signer {
    domain = msg:from_header().domain,
    selector = 'default',
    headers = { 'From', 'To', 'Subject' },
    key = 'example-private-dkim-key.pem',
  }
  msg:dkim_sign(signer)
end)