In what format should I send my webhook?

It all depends on the target system. If you do not know what kind of format your target system expects you would need to contact the provider and ask for more information.

If you are a developer, we recommend taking the default settings which is a JSON object in the payload.

You can find more related articles here:
https://support.mailparser.io/article/4131-how-do-advanced-webhooks-work
https://support.mailparser.io/article/255-what-are-webhook-integrations