SMTP

Ruby (Mail)

Use the Ruby Mail gem to send email through the Lettermint SMTP relay.

This guide covers SMTP integration. For full configuration options and available headers, see the SMTP Introduction.

Installation

Code
gem install mail

Or add to your Gemfile:

Code
gem 'mail'

Basic configuration

Use environment variables for credentials:

Code
SMTP_HOST = 'smtp.lettermint.co'
SMTP_USERNAME = 'lettermint'
API_TOKEN = ENV['LETTERMINT_PROJECT_TOKEN']

require 'mail'

Mail.defaults do
  delivery_method :smtp, {
    address: 'smtp.lettermint.co',
    port: 587,
    user_name: 'lettermint',
    password: ENV['LETTERMINT_PROJECT_TOKEN'],
    authentication: 'plain',
    enable_starttls_auto: true
  }
end

mail = Mail.new do
  from     'sender@yourdomain.com'
  to       'recipient@example.com'
  subject  'Test Email'

  text_part do
    body 'Hello! This is a test email.'
  end

  html_part do
    content_type 'text/html; charset=UTF-8'
    body '<h1>Hello!</h1><p>This is a test email.</p>'
  end
end

mail.deliver!

Advanced features

Multiple recipients

Code
mail = Mail.new do
  from     'sender@yourdomain.com'
  to       ['user1@example.com', 'user2@example.com']
  cc       'manager@yourdomain.com'
  bcc      'archive@yourdomain.com'
  subject  'Newsletter'
  body     '<h1>Monthly Update</h1>'
end

Attachments

Code
mail = Mail.new do
  from     'sender@yourdomain.com'
  to       'recipient@example.com'
  subject  'Document Attached'
  body     'Please find the document attached.'

  add_file '/path/to/document.pdf'
  add_file filename: 'data.txt', content: 'Custom content'
end

Custom headers

Code
mail = Mail.new do
  from     'sender@yourdomain.com'
  to       'recipient@example.com'
  subject  'Custom Headers'
  body     'Email with custom headers.'

  header['X-Priority'] = '1'
  header['X-Custom-Header'] = 'Custom Value'
end

Metadata for tracking

Add metadata that will be included in webhook payloads:

Code
mail = Mail.new do
  from     'sender@yourdomain.com'
  to       'recipient@example.com'
  subject  'Order Confirmation'
  body     'Your order has been confirmed.'

  header['X-LM-Metadata-order_id'] = '12345'
  header['X-LM-Metadata-customer_id'] = 'cust_789'
  header['X-LM-Metadata-campaign'] = 'order_confirmation'
end

Lettermint headers

Add Lettermint-specific headers for tags and routing:

Code
mail = Mail.new do
  from     'sender@yourdomain.com'
  to       'recipient@example.com'
  subject  'Order Confirmation'
  body     'Your order has been confirmed.'

  # Tag for categorization
  header['X-LM-Tag'] = 'order-confirmation'

  # Metadata for tracking (included in webhooks)
  header['X-LM-Metadata-order_id'] = '12345'
  header['X-LM-Metadata-customer_id'] = 'cust_789'

  # Route selection
  header['X-Lettermint-Route'] = 'transactional'
end

X-LM-Tag is the existing singular tag. For structured X-LM-Tags, use a mail library that can write repeated custom headers. See Send email with SMTP for the required syntax.

Metadata headers are extracted by Lettermint and included in webhook payloads, but not added to the actual email sent to recipients. See the SMTP Introduction for full details on available headers.

Rails integration

In config/environments/production.rb:

Code
config.action_mailer.delivery_method = :smtp
config.action_mailer.smtp_settings = {
  address: 'smtp.lettermint.co',
  port: 587,
  user_name: 'lettermint',
  password: ENV['LETTERMINT_PROJECT_TOKEN'],
  authentication: 'plain',
  enable_starttls_auto: true
}

Go SMTP Email activity