An adapter that sends email using the Resend API.

For reference:

• Sending Email API docs
• Sending Email in Batch API docs

This adapter requires an API Client. Swoosh comes with Hackney, Finch and Req out of the box. See the installation section for details.

Example

# config/config.exs
config :sample, Sample.Mailer,
  adapter: Swoosh.Adapters.Resend,
  api_key: "re_123456789"

# lib/sample/mailer.ex
defmodule Sample.Mailer do
  use Swoosh.Mailer, otp_app: :sample
end

Using with provider options

import Swoosh.Email

new()
|> from("onboarding@resend.dev")
|> to("user@example.com")
|> subject("Hello!")
|> html_body("<strong>Hello</strong>")
|> put_provider_option(:tags, [%{name: "category", value: "confirm_email"}])
|> put_provider_option(:scheduled_at, "2024-08-05T11:52:01.858Z")
|> put_provider_option(:idempotency_key, "some-unique-key-123")
|> header("X-Custom-Header", "CustomValue")

Using Templates

import Swoosh.Email

new()
|> from("onboarding@resend.dev")
|> to("user@example.com")
|> put_provider_option(:template, %{
  id: "my-template-id",
  variables: %{
    name: "John",
    action_url: "https://example.com"
  }
})

Note: When using a template, you cannot send html_body or text_body in the same email. The template's from, subject, and reply_to can be overridden in the email struct.

Inline Images

To embed images inline using Content-ID (CID):

import Swoosh.Email

new()
|> from("onboarding@resend.dev")
|> to("user@example.com")
|> subject("Welcome!")
|> html_body(~s(<h1>Hello!</h1><img src="cid:logo"/>))
|> attachment(
  Swoosh.Attachment.new(
    {:data, File.read!("logo.png")},
    filename: "logo.png",
    content_type: "image/png",
    type: :inline,
    cid: "logo"
  )
)

Provider Options

• tags (list of maps) - List of tag objects with name and value keys for categorizing emails (max 256 chars per value)

• scheduled_at (string) - ISO 8601 formatted date-time string to schedule the email for later delivery (not supported in batch sending)

• idempotency_key (string) - A unique key to prevent duplicate email sends.

• template (map) - Template object with:

  • id (required) - The ID or alias of the published template
  • variables (optional) - Map of template variables (key/value pairs)

Batch Sending

This adapter supports deliver_many/2 for sending multiple emails in a single API call using Resend's batch endpoint. Each email in the batch is independent and can have different recipients, subjects, content, and tags.

Note: The batch endpoint has a maximum of 100 emails per request and does not support scheduled_at or attachments (including inline images).