kumomta/docs/reference/events/smtp_server_message_received.md

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

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.

{{since('dev', indent=True)}} The conn_meta parameter represents the connection metadata and can be used to share state between the various SMTP listener event handlers. See Connection Metadata for more information.

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)