Henrik Bjørnskov has posted a bit of an in-depth look at Stampie, an abstraction library for sending emails from PHP applications via various service providers (like SendGrid and Mailchimp).

So what is Stampie. Stampie is a API wrapper for the most common email sending services. It provides a standard PHP Api to send emails. But mostly it is a project to test TDD and experiment with a couple of different things. Stampie is developed with Dependency Injection and therefore there is a lot of objects. At the start it can be quite cumbersome, but will make a lot of sense if you start to develop and add additional provider.

He includes a bit of sample code showing the sending of a message via the SendGrid API backend. Extending the system is simpler thanks to DI and the customizable MailerInterface object type. There's also an AdapterInterface object that can be used to redefine the HTTP connection interface the tool uses. He also points to the HBStampieBundle bundle for the Symfony2 framework that can make dropping it into your current SF2 application simpler.