Comment by bjpbakker

It migt be just me, but I honestly don't understand why people would use an HTTP API to send mail.

SMTP really is a very simple protocol, that's matured for decades now. Also it is fully specified by RFCs.

I can see why mail services that provide templating (eg Mandrill) have special APIs, they offer something different from sending regular emails.

This specific REST API seems more like a standin for sendmail, which IMO makes things only more complicated.