Sunnybox now gained support for webhooks. Besides your API you can now group Accounts into Streams and sepcify a webhook callback URL. With regards to security callback URLs must be HTTPS and can additionally be secured via BASIC AUTH.
Every stream will send emails that have not been seen before by the system (since connecting the provider to Sunnybox) as a JSON:API compliant email payload to the callback URL. For reference see the swagger docs (email) format.
In the coming days the Sunnybox Docs will be improved significantly. Stay tuned.