---
title: Capabilities and local preflight
description: Inspect supported fields and validate complete provider intent without acquiring credentials or sending.
---

Use `email.capabilities` to inspect the configured service, then call `email.validate` to apply preparation and the actual provider rules. A capability flag is a local support declaration, not a statement about account permission or remote acceptance.

## Preflight without an account

Selected provider subpaths expose credential-free functions:

```ts
import { Effect } from "effect";
import { preflightPostmarkEmail } from "@corven/email-sdk/postmark";
import { preflightResendEmail } from "@corven/email-sdk/resend";

const message = {
  body: { text: "A fictional credential-free preflight example." },
  from: "sender@fictional.invalid",
  subject: "Fictional notification",
  to: "recipient@fictional.invalid",
};

export const fictionalLocalPreflight = Effect.gen(function* inspectFictionalIntent() {
  const resend = yield* preflightResendEmail(message, { idempotencyKey: "caller-owned-event" });
  const postmark = yield* preflightPostmarkEmail(message);

  return { postmark, resend };
});
```

This example validates the same message for Resend and Postmark, but supplies a key only to Resend. Giving Postmark an unsupported key must remain a local refusal.

A preflight function needs neither credentials nor an HTTP client. It does not authenticate, inspect account settings, reserve a schedule or prevent a later remote rejection. The [CLI providers command](/reference/cli/providers) lists the available offline profiles.

## Preserve complete intent

The [field-support table](/providers/field-support) describes base profiles. Provider validation can add restrictions on mailbox formatting, body combinations, MIME types, tag syntax, header names, schedules and recipient evidence.

Do not delete a rejected field to force portability. Decide in application code whether a different message is acceptable, then prepare and approve that new intent explicitly.

## Routed candidates

Routing preflights every selected candidate's effective message, key and policy before transport. A compatible primary does not excuse an incompatible backup. The acquired routed capabilities describe common support, but they do not replace candidate validation or create cross-account replay guarantees.