# Layers and environment variables

> For the complete documentation index, see [llms.txt](https://effectkit.dev/llms.txt).

The three layer constructors every provider exports, and the environment variables each default layerConfig reads.

Source: https://effectkit.dev/docs/emails/reference/layers

Every provider subpath exports `layer`, `layerClient` and `layerConfig`. Each returns a `Layer` that provides `Email`.

| Constructor                     | Takes                                         | Client                                                                                                                 |
| ------------------------------- | --------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------- |
| `layer(options)`                | Resolved options, with secrets as `Redacted`. | Creates the SDK client and owns it. The client is closed with the layer's scope, where the SDK has something to close. |
| `layerClient(client, options?)` | A client you built.                           | Borrowed. The package never closes it, and the client keeps its own retry, timeout and logging policy.                 |
| `layerConfig(config?)`          | An Effect `Config` of the options.            | As `layer`.                                                                                                            |

`layerConfig` has a default `Config` that reads the environment variables below. Mailtrap has no default, so its `config` argument is required.

**Example** (Reading Environment Variables With the Default Config)

```ts twoslash
import { ConfigProvider, Effect, Layer } from "effect";
import { Email } from "@effect-kit/emails";
import * as Resend from "@effect-kit/emails/resend";

const EmailLive = Resend.layerConfig().pipe(
  Layer.provide(ConfigProvider.layer(ConfigProvider.fromEnv())),
);

const program = Effect.gen(function* () {
  const email = yield* Email;
  return email.provider;
}).pipe(Effect.provide(EmailLive));
```

Layer errors are typed: `layerConfig` can fail with `Config.ConfigError` for a missing or malformed variable, and every constructor can fail with the provider's configuration error. See [Errors](/docs/emails/reference/errors#configuration-errors).

`Redacted` secrets must be printable ASCII with no whitespace. Every provider accepts a `timeout` option of a finite, positive `Duration`. The default is 30 seconds, and 60 seconds for `azure`.

## Environment variables [#environment-variables]

These are the variables the default `layerConfig` reads.

| Provider                  | Variables                                                                                           |
| ------------------------- | --------------------------------------------------------------------------------------------------- |
| `resend`                  | `RESEND_API_KEY`                                                                                    |
| `nodemailer`              | `SMTP_HOST`, `SMTP_PORT` (default 587), `SMTP_SECURE` (default false), `SMTP_USER`, `SMTP_PASSWORD` |
| `ses`                     | `AWS_REGION`                                                                                        |
| `azure`                   | `AZURE_EMAIL_CONNECTION_STRING`                                                                     |
| `postmark`                | `POSTMARK_SERVER_TOKEN`                                                                             |
| `sendgrid`                | `SENDGRID_API_KEY`                                                                                  |
| `mailgun`                 | `MAILGUN_API_KEY`, `MAILGUN_DOMAIN`, `MAILGUN_REGION` (`us` or `eu`)                                |
| `mailersend`              | `MAILERSEND_API_KEY`                                                                                |
| `brevo`                   | `BREVO_API_KEY`                                                                                     |
| `mailtrap`                | none, pass a `Config`                                                                               |
| `scaleway`                | `SCW_ACCESS_KEY`, `SCW_SECRET_KEY`, `SCW_PROJECT_ID`, `SCW_REGION` (`fr-par`)                       |
| `lettermint`              | `LETTERMINT_SENDING_TOKEN`                                                                          |
| `eusend`                  | `EUSEND_API_KEY`                                                                                    |
| `zeptomail`               | `ZEPTOMAIL_TOKEN`, `ZEPTOMAIL_URL`                                                                  |
| `mailchimp-transactional` | `MAILCHIMP_TRANSACTIONAL_API_KEY`                                                                   |
| `plunk`                   | `PLUNK_API_KEY`                                                                                     |

The default `nodemailer` config requires `SMTP_USER` and `SMTP_PASSWORD`. For an SMTP server without authentication, use `Nodemailer.layer` with a `transport` that has no `auth`.

Options the default config does not read, such as `baseUrl`, `messageStream`, `sandbox` or SES `credentials`, need a custom `Config` or `layer`.

## Options by provider [#options-by-provider]

`timeout` is accepted everywhere and is omitted below.

| Provider                  | `layer` options                                                                                                                                                          |
| ------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `resend`                  | `apiKey`, `baseUrl?`                                                                                                                                                     |
| `nodemailer`              | `transport` (`host`, `port?`, `secure?`, `requireTLS?`, `auth?`, `pool?`, `maxConnections?`, `maxMessages?`, `connectionTimeout?`, `greetingTimeout?`, `socketTimeout?`) |
| `ses`                     | `region`, `credentials?`, `endpoint?`, `configurationSetName?`                                                                                                           |
| `azure`                   | `connectionString`, `pollInterval?`                                                                                                                                      |
| `postmark`                | `serverToken`, `messageStream?`                                                                                                                                          |
| `sendgrid`                | `apiKey`                                                                                                                                                                 |
| `mailgun`                 | `apiKey`, `domain`, `region`, `endpoint?`                                                                                                                                |
| `mailersend`              | `apiKey`                                                                                                                                                                 |
| `brevo`                   | `apiKey`                                                                                                                                                                 |
| `mailtrap`                | `token`, `mode`, `inboxId` (a number, required for `sandbox`, not allowed otherwise)                                                                                     |
| `scaleway`                | `accessKey`, `secretKey`, `projectId`, `region`                                                                                                                          |
| `lettermint`              | `sendingToken`, `sandbox?`                                                                                                                                               |
| `eusend`                  | `apiKey`, `baseUrl?`                                                                                                                                                     |
| `zeptomail`               | `token`, `url`                                                                                                                                                           |
| `mailchimp-transactional` | `apiKey`, `baseUrl?`                                                                                                                                                     |
| `plunk`                   | `apiKey`, `baseUrl?`                                                                                                                                                     |

## `layerClient` options [#layerclient-options]

The second argument is optional for every provider except these three, where it holds required fields.

| Provider   | Required options      |
| ---------- | --------------------- |
| `mailgun`  | `domain`              |
| `mailtrap` | `mode`                |
| `scaleway` | `projectId`, `region` |