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Outbound Mail with Haraka

A default installation of Haraka will queue outbound mail for delivery in the queue directory. Those mails will be delivered to the appropriate MX record for that domain. Mails are queued onto your disk, and will deal appropriately with temporary failures to retry delivery later.

Outbound mails are defined as those that have set the connection.relaying flag to true via a plugin. The simplest way of doing that is to use SMTP AUTH, and have the client authenticate. For example using the auth/flat_file plugin. However it is very simple to write a custom plugin to do this.

Outbound Configuration Files

outbound.concurrency_max

Default: 100. Specifies the maximum concurrent connections to make. Note that if using cluster (multiple CPUs) then this will be multiplied by the number of CPUs that you have.

outbound.enable_tls

Default: 0. Put a "1" in this file to enable TLS for outbound mail when the remote end is capable of receiving TLS connections.

This uses the same tls_key.pem and tls_cert.pem files that the tls plugin uses. See the plugin documentation for information on generating those files.

outbound.bounce_message

See "Bounce Messages" below for details.

outbound.disabled

Allows you to temporarily disable outbound delivery, while still able to receive and queue emails. This can be done while Haraka is running due to how Haraka watches for config file changes.

Outbound Mail Hooks

The queue_outbound hook

The first hook that is called prior to queueing an outbound mail is the queue_outbound hook. Only if all these hooks return CONT (or if there are no hooks) will the mail be queued for outbound delivery. A return of OK will indicate that the mail has been queued in some custom manner for outbound delivery. Any of the DENY return codes will cause the message to be appropriately rejected.

The get_mx hook

Upon starting delivery the get_mx hook is called, with the parameter set to the domain in question (for example a mail to user@example.com will call the get_mx hook with (next, hmail, domain) as parameters). This is to allow you to implement a custom handler to find MX records. For most installations there is no reason to implement this hook - Haraka will find the correct MX records for you.

The MX record is sent via next(OK, mx) and can be one of:

  • A string of one of the following formats:
    • hostname
    • hostname:port
    • ipaddress
    • ipaddress:port
  • An MX object of the form: {priority: 0, exchange: hostname} and optionally a port value to specify an alternate port.
  • A list of MX objects in an array.

The bounce hook

If the mail completely bounces then the bounce hook is called. This is not called if the mail is issued a temporary failure (a 4xx error code). The hook parameter is the error message received from the remote end. If you do not wish to have a bounce message sent to the originating sender of the email then you can return OK from this hook to stop it from sending a bounce message.

The delivered hook

When mails are successfully delivered to the remote end then the delivered hook is called. The return codes from this hook have no effect, so it is only useful for logging the fact that a successful delivery occurred. This hook is called with (hmail, response) as parameters, the response variable contains the SMTP response text returned by the host that received the message and will typically contain the remote queue ID.

Bounce Messages

The contents of the bounce message are configured by a file called config/outbound.bounce_message. If you look at this file you will see it contains several template entries wrapped in curly brackets. These will be populated as follows:

  • pid - the current process id
  • date - the current date when the bounce occurred
  • me - the contents of config/me
  • from - the originating sender of the message
  • msgid - a uuid for the mail
  • to - the end recipient of the message, or the first recipient if it was to multiple people
  • reason - the text from the remote server indicating why it bounced

Following the bounce message itself will be a copy of the entire original message.

Creating a mail internally for outbound delivery

Sometimes it is necessary to generate a new mail from within a plugin.

To do that, you can use the outbound module directly:

var outbound = require('./outbound');

var plugin = this;

var to = 'user@example.com';
var from = 'sender@example.com';

var contents = [
    "From: " + from,
    "To: " + to,
    "MIME-Version: 1.0",
    "Content-type: text/plain; charset=us-ascii",
    "Subject: Some subject here",
    "",
    "Some email body here",
    ""].join("\n");
    
var outnext = function (code, msg) {
    switch (code) {
        case DENY:  plugin.logerror("Sending mail failed: " + msg);
                    break;
        case OK:    plugin.loginfo("mail sent");
                    next();
                    break;
        default:    plugin.logerror("Unrecognised return code from sending email: " + msg);
                    next();
    }
};

outbound.send_email(from, to, contents, outnext);

The callback on send_email() is passed OK if the mail is successfully queued to disk, not when it is successfully delivered. To check delivery status you still need to hook delivered and bounce to know if it was successfully delivered.

The callback parameter may be omitted if you don't need to handle errors should queueing to disk fail e.g:

outbound.send_email(form, to, contents);