Choosing a provider

All 16 providers share the Email service, but they do not support the same message features. The package checks the message against the provider's capabilities first, and fails with UnsupportedFeatureError before any request when a feature is missing.

Example (Changing the Provider Without Changing the Program)

import { Effect } from "effect";
import { Email } from "@effect-kit/emails";
import * as Resend from "@effect-kit/emails/resend";

const program = Effect.gen(function* () {
  const email = yield* Email;
  return yield* email.send({
    from: "hello@example.com",
    to: "ada@example.com",
    subject: "Welcome",
    text: "Your account is ready.",
  });
});

Effect.runPromise(program.pipe(Effect.provide(Resend.layerConfig())));

What differs

Every provider supports text, HTML, both together, cc, bcc and custom headers, except Plunk. The rest of the differences:

Provider	Reply-to	Attachments	Inline images	Sender name	Idempotency
`resend`	multiple	yes	yes	yes	replay, 24 hours
`nodemailer`	multiple	yes	yes	yes	no
`ses`	multiple	yes	yes	yes	no
`azure`	multiple	yes	yes	no	no
`postmark`	multiple	yes	yes	yes	no
`sendgrid`	one	yes	yes	yes	no
`mailgun`	multiple	yes	no	yes	no
`mailersend`	one	no	no	yes	no
`brevo`	one	no	no	yes	reject, 30 minutes
`mailtrap`	one	yes	yes	yes	no
`scaleway`	multiple	yes	no	yes	no
`lettermint`	multiple	yes	yes	yes	replay, 24 hours
`eusend`	multiple	yes	yes	yes	replay
`zeptomail`	multiple	yes	yes	yes	no
`mailchimp-transactional`	multiple	yes	no	yes	no
`plunk`	none	no	no	yes	no

Only Resend, Lettermint, eusend and Brevo support idempotency keys. On any other provider, a message sent with an idempotencyKey fails with UnsupportedFeatureError before sending. Lettermint inline images need a content id that contains @.

Plunk is HTML only

Plunk sends HTML with exactly one to address and no name. It has no text body, cc, bcc, reply-to, headers or attachments, so any of those fail with UnsupportedFeatureError.

Read these at runtime from email.capabilities, and see the provider overview for the full matrix.

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What differs