This release packs some stability improvements (notably related to custom headers) and new features.
Most important new feature is templating support. You can now create a template based sending function by providing a template or an external template renderer and that’s it, you can start sending by providing only the template context to this function. Read more about the template support here.
The other new feature is support for 'idle' events and isIdle() method to be able to manage large queues more effectively. Here’s an example for using RabbitMQ based queues when sending mail.