> ## Documentation Index
> Fetch the complete documentation index at: https://resend.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Send emails with Sinatra

> Learn how to send your first email using Sinatra and the Resend Ruby SDK.

## Prerequisites

Before you start, you'll need:

* A Resend [API key](/create-an-api-key)
* A [verified domain](/add-a-domain)

## 1. Install

Get the Resend Ruby SDK.

<CodeGroup>
  ```bash RubyGems theme={"theme":{"light":"github-light","dark":"vesper"}}
  gem install resend
  ```

  ```bash Gemfile theme={"theme":{"light":"github-light","dark":"vesper"}}
  gem 'resend'
  ```
</CodeGroup>

## 2. Send email using HTML

The easiest way to send an email is by using the `html` parameter.

```rb index.rb theme={"theme":{"light":"github-light","dark":"vesper"}}
require "sinatra"
require "resend"

set :port, 5000
set :bind, "0.0.0.0"

Resend.api_key = ENV["RESEND_API_KEY"]

get "/" do

  content_type :json

  params = {
    from: 'Acme <onboarding@resend.dev>',
    to: ['delivered@resend.dev'],
    subject: 'hello world',
    html: '<strong>it works!</strong>',
  }

  Resend::Emails.send(params).to_hash.to_json
end
```

## 3. Try it yourself

<CardGroup cols={3}>
  <Card title="Sinatra App" icon="arrow-up-right-from-square" href="https://github.com/resend/resend-examples/tree/main/ruby-resend-examples/sinatra_app">
    Full Sinatra web application
  </Card>

  <Card title="Basic Send" icon="arrow-up-right-from-square" href="https://github.com/resend/resend-examples/blob/main/ruby-resend-examples/examples/basic_send.rb">
    Basic email sending
  </Card>

  <Card title="Attachments" icon="arrow-up-right-from-square" href="https://github.com/resend/resend-examples/blob/main/ruby-resend-examples/examples/with_attachments.rb">
    Send emails with file attachments
  </Card>

  <Card title="Templates" icon="arrow-up-right-from-square" href="https://github.com/resend/resend-examples/blob/main/ruby-resend-examples/examples/with_template.rb">
    Send emails using Resend hosted templates
  </Card>

  <Card title="Scheduling" icon="arrow-up-right-from-square" href="https://github.com/resend/resend-examples/blob/main/ruby-resend-examples/examples/scheduled_send.rb">
    Schedule emails for future delivery
  </Card>

  <Card title="Audiences" icon="arrow-up-right-from-square" href="https://github.com/resend/resend-examples/blob/main/ruby-resend-examples/examples/audiences.rb">
    Manage contacts and audiences
  </Card>

  <Card title="Domains" icon="arrow-up-right-from-square" href="https://github.com/resend/resend-examples/blob/main/ruby-resend-examples/examples/domains.rb">
    Create and manage sending domains
  </Card>

  <Card title="Inbound Webhooks" icon="arrow-up-right-from-square" href="https://github.com/resend/resend-examples/blob/main/ruby-resend-examples/examples/inbound.rb">
    Receive and process inbound emails
  </Card>

  <Card title="Double Opt-in" icon="arrow-up-right-from-square" href="https://github.com/resend/resend-examples/tree/main/ruby-resend-examples/examples/double_optin">
    Double opt-in subscription flow
  </Card>
</CardGroup>