For those wondering why I didn't bother with
postfix plugins from the get-go...
I'm of the opinion that email sending has become much more complicated since the time of those programs. With DKIM and SPF almost a necessity, allowing forum admins to send email through a local (or remote SMTP) server means I would eventually have to deal with users wondering why they're seeing a bounce rate of > 50%.
PostageApp is the first plugin, mostly because they are Canadian, as is the NodeBB team. Don't worry, the other plugins will come along soon