Everything a form backend should do, and the routing most of them skip.
Postbag receives forms, stores every submission durably, and delivers each one by rules. Six capabilities carry the product; each has its own page with specifics, code and limits.
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Routing and streams
A route sends a form, or a whole stream of forms, to a destination with rules. Streams are how an operator turns fifteen slightly different contact forms into one contract a partner can rely on.
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Durable delivery
The HTTP 200 is your receipt. Nothing in the write path talks to a third party, and nothing that goes wrong later can reach back and lose what was received.
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Destinations
A destination is somewhere submissions can go. Destinations are organization-level and reusable across routes, and every one of them can be tested from the API before it is trusted.
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Schemas and drift
A form schema is a versioned declaration of what a form collects. You never have to write one, but when you run many sites you want to know the moment one of them changes.
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Spam protection
Defence in depth, none of it destructive. Spam is a label you can see and flip, not a bin you cannot open.
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Self-hosting
The hosted product is the same image with billing turned on. No feature may depend on a cloud-only service without a self-host path; that is a principle, not a roadmap item.
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And a dashboard that is just another API client.
Forms, a live inbox, destinations, routes, streams (shown as Bags), deliveries, events and API keys. Everything it does goes through the same /v1 an agent uses; there is no UI-only capability.
What is a form backend?
A form backend is a hosted endpoint that receives HTML form submissions so a website does not need server code of its own. The site's <form action> points at the backend; the backend stores the submission and notifies someone. Postbag is a form backend that also routes: it can group many forms into one stream, map their differing fields onto one versioned schema, and deliver that shape to several destinations with rules, while keeping every submission as a durable row. It is multi-tenant, self-hostable, and driven entirely through one API so that AI agents can set it up without a browser.
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