Sorry for the late answer: I am using GitHub - danielireson/formplug: Form forwarding service for AWS Lambda at the moment. But on the last strapi conf was the customization workshop (Strapi internals, customizing the Strapi backend) where Richard showed how to limit the request per minute with a koa js npm-package. I hope the recording is available soon. This could be a way to use strapi as a formmailer.