I think SMTP is the way to go unless you're actually using specific proprietary mailer API features and there's no way to do the same via SMTP.

Solution is:

* SMTP by default

* if you want, some setup examples of using third-party mail services using their SMTP endpoint (most offer one)

Again you don't have to, it's an open-source project and you owe nothing to anyone. But if you fancy doing it, this is the way to go and will save headaches later.