SMTP is a must. My advice is to never bother with proprietary mailer APIs - you will need to change providers sooner or later (sometimes on short notice, if your current provider temporarily suspended you on a false positive for example), which is much easier when you just need to swap the SMTP credentials vs implementing yet another proprietary API. Plus it makes local testing easier - there's no shortage of "fake SMTP for development" projects out there.
Of course, tech bros don't want you to do it, as it reduces their vendor lock-in.
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.
And just remember the more HAM you send out to different domains and not SPAM, the better the IP gets overtime. And then BAM you got your own little self hosted poormans mailchimp.
Of course, tech bros don't want you to do it, as it reduces their vendor lock-in.