When sending email from your application, using queuing process can reduce the application response time and increase speed.

By sending the message to queue instead of sending directly at the end of server response, you may achieve better user experience. Once messages are in queue, you just need a scheduled cron task to initiate scheduled email sending.

How ?

Queuing is simple in Drupal 8

Let's imagine you have a module that currently send an email using mail plugin to multiple users:

foreach (User::loadMultiple($users) as $account) {
    \Drupal::service('plugin.manager.mail')->mail(
            'my_module,
            'my_key',
            $account->getEmail(),
            $account->getPreferredLangcode(),
            $params,
            $from->mail,
            TRUE
         );
}

To direct message to queue instead, you can replace with queue service:

In previous article we explained how we installed the Swift Mailer module and its dependencies.

In this second part, let's see how we configure and implement it to use in our modules to send formated HTML mail with attachment.

First you will need to have Mail system module installed already. There is no particular issue or difficulty here.

1) Configure Swift Mailer

In Swift Mailer configuration (/admin/config/swiftmailer/transport) , we select the following options:

Transport:

In a previous post from 2015, we described usage of Swift Mailer module to send HTML mail and mail with attachment. At this time, the module was not yet available for Drupal 8.

There is now a version alpha1 available. Let's go through installation process.

Because it has been rather tedious for us, we will try to explain the flow of the process as much as possible to help you save time.

1) Composer

The prerequisite is the installation of composer.

In our case we installed first on Windows inside a folder named  F:\Program Files\composer2\.

The installation exe for Windows can be found here.