What is the missing sauce? My understanding is that once your sending IP has some history and has developed a reputation as not sending spam, there isn't anything offered by Sendgrid that improves upon that.
If you set up SPF and Domainkeys/DKIM that is an added vote of confidence but Sendgrid doesn't even require it, so I think most of the value of Sendgrid is simply offering a stable IP address and a convenient API. Am I wrong?
Read here: https://news.ycombinator.com/item?id=18225068
That poster gave a very detailed breakdown, but point #1 is enough to make anyone who’s done this before cry in a corner from the abuse they endured.
Yes. No matter what your project is, unless your secret sauce has to do with email delivery or your business model requires email delivery to be free, do not attempt to roll your own email delivery service. No one has ever looked back and wished they had.