I use simply static have since before the Appsumo launch and have been using formspree i wanted something I could use with it to deliver emails from Simply Static sites without paying form spree, now there is no native integration Patrick has said he will add bearer tokens to it in future so we may get a native integration but I have built a (Form processor) using Fluent SMTP and Flowmattic that allows me to now deliver emails form my static site through email it, it works I have a dedicated domain for delivering those emails now which will only be used with those webforms, I went all out on this one as I want to grow with it.

It would be nice to see native integration with simply static but until then I will use my Flowmattic solution, you can see how I've built my integration here https://www.youtube.com/watch?v=-DmQmekI5Xc and it should work in similar ways with Pabbly, make and Zapier

In addition this, I have added it to a couple of my sites for transactional delivery and once setup it works, George was brilliant reached out to me personally... Its early days but if this keeps developing and delivering it will be nice to get a good one

I am not a current heavy user so can't talk about volumes and or longevity but in my testing and building they have delivered really quite well with a brand new domain, adding the domain was painless and took seconds