If you deploy with Netlify, they have a form handling service.
Netlify’s form handling is as simple as could be – just add a form and a data attribute to it, and they will handle the data. You can easily use post hooks to send it to Zapier and then on to wherever (I use it to send to a Mailchimp list)
I personally use and recommend https://www.formata.io it’s been great for us since we manage like 75+ sites, most of them are static sites and we need something reliable that can handle hundreds of requests per month. Give it a try it’s the best we have used so far
I developed a simple solution for that purpose https://kamilsk.github.io/form-api/. It is open source, free and can be self-hosted. The main disadvantage that it is MVP now and can handle only simple forms (email, text).
Thanks for sharing me cool services for inspiration!
In the end, as you say Hugo is a SSG, and it just assembles what you give it into a website, so, you can use whatever form processing system you like. There are many.