Mailer Generator

Generate email functionality using the Carbon email library with support for HTML/text templates and async delivery via background jobs.

Synopsis

azu generate mailer <name> [methods...] [options]

Description

The mailer generator creates email functionality for your Azu application using the Carbon email library. It generates mailer classes with methods for sending emails, template files for email content, and optional background job integration for async email delivery.

Features

• 📧 HTML & Text Emails: Dual-format support for all email clients

• 🎨 Template System: Jinja/ECR templates for email content

• 🚀 Async Delivery: Background job integration via JoobQ

• 🔧 Multiple Adapters: SMTP, SendGrid, development, and custom adapters

• 📎 Attachments: File attachment support

• 🔐 Secure: Built-in security best practices

• 🧪 Testable: Easy to test email functionality

Usage

Basic Usage

Generate a mailer with default welcome email:

azu generate mailer User

This creates:

• src/mailers/user_mailer.cr - Mailer class

• src/mailers/templates/user/welcome.text.ecr - Plain text template

• src/mailers/templates/user/welcome.html.ecr - HTML template

Custom Email Methods

Generate mailer with specific email methods:

azu generate mailer User welcome password_reset email_confirmation

Common Mailer Types

User Notifications

azu generate mailer User welcome password_reset email_confirmation

Order/Transaction Emails

azu generate mailer Order confirmation shipped delivered

Newsletter/Marketing

azu generate mailer Newsletter weekly_digest promotional announcement

System Notifications

azu generate mailer System error_alert backup_complete security_notice

Arguments

Argument	Type	Description	Required
<name>	string	Mailer name (PascalCase)	Yes
[methods...]	strings	Email method names	No (defaults to welcome)

Options

Option	Description	Default
--async	Enable async delivery	true
--no-async	Disable async delivery
--force	Overwrite existing files	false

Generated Files

Directory Structure

src/
├── mailers/
│   ├── user_mailer.cr                      # Mailer class
│   ├── templates/
│   │   └── user/
│   │       ├── welcome.text.ecr            # Plain text template
│   │       ├── welcome.html.ecr            # HTML template
│   │       ├── password_reset.text.ecr
│   │       └── password_reset.html.ecr
│   └── base_mailer.cr                      # Base mailer (if not exists)
└── jobs/
    └── user_mailer_job.cr                  # Async delivery job (if --async)

Mailer Class

require "carbon"
require "../base_mailer"

# User mailer for user-related emails
class UserMailer < BaseMailer
  # Send welcome email
  def welcome(to email : Carbon::Address, **params)
    welcome_email(to: email, **params)
  end

  private def welcome_email(to email : Carbon::Address, **params)
    Carbon::Email.new(
      to: email,
      from: Carbon::Address.new(from_email, from_name),
      subject: "Welcome",
      text_body: render_text("user/welcome", params),
      html_body: render_html("user/welcome", params)
    )
  end

  # Send password reset email
  def password_reset(to email : Carbon::Address, **params)
    password_reset_email(to: email, **params)
  end

  private def password_reset_email(to email : Carbon::Address, **params)
    Carbon::Email.new(
      to: email,
      from: Carbon::Address.new(from_email, from_name),
      subject: "Password Reset",
      text_body: render_text("user/password_reset", params),
      html_body: render_html("user/password_reset", params)
    )
  end

  # Deliver welcome email asynchronously
  def welcome_later(to email : Carbon::Address, **params)
    UserMailerJob.perform_later(
      action: "welcome",
      to: email.to_s,
      params: params.to_h
    )
  end

  # Deliver password reset email asynchronously
  def password_reset_later(to email : Carbon::Address, **params)
    UserMailerJob.perform_later(
      action: "password_reset",
      to: email.to_s,
      params: params.to_h
    )
  end
end

Base Mailer

require "carbon"

# Base mailer with common configuration and helpers
abstract class BaseMailer
  # Default from email
  def from_email : String
    ENV["FROM_EMAIL"]? || "[e-mail]"
  end

  # Default from name
  def from_name : String
    ENV["FROM_NAME"]? || "My App"
  end

  # Render plain text template
  def render_text(template : String, params : NamedTuple) : String
    path = "src/mailers/templates/#{template}.text.ecr"
    ECR.render(path)
  end

  # Render HTML template
  def render_html(template : String, params : NamedTuple) : String
    path = "src/mailers/templates/#{template}.html.ecr"
    ECR.render(path)
  end

  # Helper: Format currency
  def format_currency(amount : Float64) : String
    "$%.2f" % amount
  end

  # Helper: Format date
  def format_date(date : Time) : String
    date.to_s("%B %d, %Y")
  end
end

Email Templates

HTML Template (welcome.html.ecr)

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Welcome to <%= params[:app_name] %></title>
    <style>
      body {
        font-family: Arial, sans-serif;
        line-height: 1.6;
        color: #333;
        max-width: 600px;
        margin: 0 auto;
        padding: 20px;
      }
      .header {
        background-color: #007bff;
        color: white;
        padding: 20px;
        text-align: center;
      }
      .content {
        padding: 30px 20px;
      }
      .button {
        display: inline-block;
        padding: 12px 30px;
        background-color: #007bff;
        color: white;
        text-decoration: none;
        border-radius: 5px;
        margin: 20px 0;
      }
      .footer {
        text-align: center;
        color: #666;
        font-size: 12px;
        padding: 20px;
        border-top: 1px solid #ddd;
      }
    </style>
  </head>
  <body>
    <div class="header">
      <h1>Welcome to <%= params[:app_name] %>!</h1>
    </div>

    <div class="content">
      <p>Hi <%= params[:user_name] %>,</p>

      <p>Thank you for signing up! We're excited to have you on board.</p>

      <p>
        To get started, please confirm your email address by clicking the button
        below:
      </p>

      <p style="text-align: center;">
        <a href="<%= params[:confirmation_url] %>" class="button">
          Confirm Email Address
        </a>
      </p>

      <p>
        If the button doesn't work, you can also copy and paste this link into
        your browser:
      </p>
      <p><%= params[:confirmation_url] %></p>

      <p>If you didn't create an account, you can safely ignore this email.</p>

      <p>
        Best regards,<br />
        The <%= params[:app_name] %> Team
      </p>
    </div>

    <div class="footer">
      <p>This email was sent to <%= params[:user_email] %></p>
      <p><%= params[:app_name] %> | <%= params[:company_address] %></p>
    </div>
  </body>
</html>

Text Template (welcome.text.ecr)

Welcome to <%= params[:app_name] %>!

Hi <%= params[:user_name] %>,

Thank you for signing up! We're excited to have you on board.

To get started, please confirm your email address by visiting:
<%= params[:confirmation_url] %>

If you didn't create an account, you can safely ignore this email.

Best regards,
The <%= params[:app_name] %> Team

---
This email was sent to <%= params[:user_email] %>
<%= params[:app_name] %> | <%= params[:company_address] %>

Async Job (with --async)

require "joobq"
require "../mailers/user_mailer"

# Background job for async email delivery
struct UserMailerJob
  include JoobQ::Job

  queue "mailers"

  property action : String
  property to : String
  property params : Hash(String, String)

  def perform
    email_address = Carbon::Address.new(to)
    mailer = UserMailer.new

    case action
    when "welcome"
      email = mailer.welcome(email_address, **named_tuple_from_hash(params))
      email.deliver
    when "password_reset"
      email = mailer.password_reset(email_address, **named_tuple_from_hash(params))
      email.deliver
    else
      raise "Unknown mailer action: #{action}"
    end

    Log.info { "Delivered #{action} email to #{to}" }
  end

  private def named_tuple_from_hash(hash : Hash(String, String))
    hash.transform_keys(&.to_sym)
  end
end

Email Adapter Configuration

Development Adapter

Prints emails to console (no external services required):

# src/config/carbon.cr
Carbon::DevAdapter.configure do |settings|
  settings.print_emails = true
end

SMTP Adapter

For production use with any SMTP server:

Carbon::SmtpAdapter.configure do |settings|
  settings.host = ENV["SMTP_HOST"]
  settings.port = ENV["SMTP_PORT"].to_i
  settings.username = ENV["SMTP_USERNAME"]
  settings.password = ENV["SMTP_PASSWORD"]
  settings.use_tls = true
end

SendGrid Adapter

For SendGrid email service:

Carbon::SendGridAdapter.configure do |settings|
  settings.api_key = ENV["SENDGRID_API_KEY"]
end

Custom Adapter

Create your own adapter:

class MyCustomAdapter < Carbon::Adapter
  def deliver(email : Carbon::Email)
    # Your delivery logic
  end
end

Carbon.adapter = MyCustomAdapter.new

Usage Examples

Send Welcome Email

# Synchronous delivery
mailer = UserMailer.new
email = mailer.welcome(
  to: Carbon::Address.new("[e-mail]", "John Doe"),
  user_name: "John",
  app_name: "My App",
  confirmation_url: "https://app.com/confirm/abc123",
  user_email: "[e-mail]",
  company_address: "123 Main St, City, State 12345"
)
email.deliver

# Asynchronous delivery (via background job)
mailer.welcome_later(
  to: Carbon::Address.new("[e-mail]", "John Doe"),
  user_name: "John",
  app_name: "My App",
  confirmation_url: "https://app.com/confirm/abc123",
  user_email: "[e-mail]",
  company_address: "123 Main St, City, State 12345"
)

Send Password Reset

user = User.find_by_email("[e-mail]")
token = generate_password_reset_token(user)

OrderMailer.new.password_reset_later(
  to: Carbon::Address.new(user.email, user.name),
  user_name: user.name,
  reset_url: "https://app.com/reset/#{token}",
  expiry_time: "24 hours"
)

Send Order Confirmation

order = Order.find(order_id)

OrderMailer.new.confirmation_later(
  to: Carbon::Address.new(order.customer_email, order.customer_name),
  order_id: order.id.to_s,
  order_total: format_currency(order.total),
  order_items: order.items.map(&.to_json),
  tracking_url: "https://app.com/orders/#{order.id}"
)

Send with Attachments

mailer = InvoiceMailer.new
email = mailer.invoice(
  to: Carbon::Address.new("[e-mail]"),
  invoice_number: "INV-001"
)

# Add PDF attachment
pdf_data = generate_invoice_pdf(invoice)
email.attach(
  file_name: "invoice-001.pdf",
  data: pdf_data,
  mime_type: "application/pdf"
)

email.deliver

Advanced Features

Multiple Recipients

email = UserMailer.new.newsletter(
  to: [
    Carbon::Address.new("[e-mail]"),
    Carbon::Address.new("[e-mail]"),
    Carbon::Address.new("[e-mail]")
  ],
  subject: "Monthly Newsletter",
  content: newsletter_content
)

CC and BCC

email.cc = [Carbon::Address.new("[e-mail]")]
email.bcc = [Carbon::Address.new("[e-mail]")]

Custom Headers

email.headers["X-Custom-Header"] = "custom-value"
email.headers["X-Priority"] = "high"

Reply-To

email.reply_to = Carbon::Address.new("[e-mail]", "Support Team")

Email Priorities

# High priority
email.headers["X-Priority"] = "1"
email.headers["Importance"] = "high"

# Low priority
email.headers["X-Priority"] = "5"
email.headers["Importance"] = "low"

Template Helpers

Common Helpers

Add to BaseMailer:

abstract class BaseMailer
  # Format money
  def format_money(amount : Float64, currency : String = "USD") : String
    case currency
    when "USD"
      "$%.2f" % amount
    when "EUR"
      "€%.2f" % amount
    else
      "#{currency} %.2f" % amount
    end
  end

  # Format date
  def format_date(date : Time, format : String = "%B %d, %Y") : String
    date.to_s(format)
  end

  # Pluralize
  def pluralize(count : Int32, singular : String, plural : String? = nil) : String
    plural ||= "#{singular}s"
    count == 1 ? "#{count} #{singular}" : "#{count} #{plural}"
  end

  # Truncate
  def truncate(text : String, length : Int32 = 100, suffix : String = "...") : String
    text.size <= length ? text : "#{text[0...length]}#{suffix}"
  end

  # Link button
  def link_button(text : String, url : String, color : String = "#007bff") : String
    <<-HTML
    <a href="#{url}" style="display: inline-block; padding: 12px 30px; background-color: #{color}; color: white; text-decoration: none; border-radius: 5px;">
      #{text}
    </a>
    HTML
  end
end

Testing

Unit Tests

require "../spec_helper"

describe UserMailer do
  describe "#welcome" do
    it "creates welcome email" do
      mailer = UserMailer.new
      email = mailer.welcome(
        to: Carbon::Address.new("[e-mail]", "Test User"),
        user_name: "Test",
        app_name: "Test App",
        confirmation_url: "https://test.com/confirm/abc",
        user_email: "[e-mail]",
        company_address: "Test Address"
      )

      email.to.first.address.should eq("[e-mail]")
      email.subject.should eq("Welcome")
      email.html_body.should contain("Test User")
      email.html_body.should contain("https://test.com/confirm/abc")
    end
  end

  describe "#password_reset" do
    it "creates password reset email" do
      mailer = UserMailer.new
      email = mailer.password_reset(
        to: Carbon::Address.new("[e-mail]"),
        user_name: "Test",
        reset_url: "https://test.com/reset/token"
      )

      email.subject.should eq("Password Reset")
      email.html_body.should contain("reset/token")
    end
  end
end

Integration Tests

describe "Email delivery" do
  it "delivers welcome email asynchronously" do
    user = create_user(email: "[e-mail]")

    UserMailer.new.welcome_later(
      to: Carbon::Address.new(user.email, user.name),
      user_name: user.name,
      # ...
    )

    # Check job was enqueued
    UserMailerJob.queue.size.should eq(1)

    # Process job
    UserMailerJob.process_queue

    # Check email was delivered (using test adapter)
    Carbon::DevAdapter.emails.size.should eq(1)
    email = Carbon::DevAdapter.emails.first
    email.to.first.address.should eq(user.email)
  end
end

Best Practices

1. Use Plain Text + HTML

Always provide both formats:

Carbon::Email.new(
  # ...
  text_body: render_text("template"),
  html_body: render_html("template")
)

2. Personalize Emails

Use recipient's name:

<p>Hi <%= params[:user_name] %>,</p>

3. Clear Call-to-Action

Make primary action obvious:

<p style="text-align: center;">
  <a href="<%= params[:action_url] %>" class="button"> Take Action Now </a>
</p>

4. Responsive Design

Use mobile-friendly HTML:

<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<style>
  @media only screen and (max-width: 600px) {
    .content {
      padding: 10px;
    }
  }
</style>

5. Unsubscribe Links

Always include for marketing emails:

<p>
  <a href="<%= params[:unsubscribe_url] %>">Unsubscribe</a>
</p>

6. Test in Multiple Clients

Test emails in:

• Gmail

• Outlook

• Apple Mail

• Mobile devices

7. Monitor Delivery

Track:

• Delivery rate

• Open rate

• Click rate

• Bounce rate

Environment Configuration

Add to .env:

# From Email
FROM_EMAIL=[e-mail]
FROM_NAME=Your App Name

# SMTP Configuration
SMTP_HOST=smtp.example.com
SMTP_PORT=587
SMTP_USERNAME=your-username
SMTP_PASSWORD=your-password

# SendGrid (alternative)
SENDGRID_API_KEY=your-sendgrid-api-key

# Company Info
COMPANY_NAME=Your Company
COMPANY_ADDRESS=123 Main St, City, State 12345
SUPPORT_EMAIL=[e-mail]

Dependencies

Add to shard.yml:

dependencies:
  carbon:
    github: luckyframework/carbon
    version: ~> 0.4.0

  # For async delivery
  joobq:
    github: azutoolkit/joobq

Troubleshooting

Emails Not Sending

Check adapter configuration:

pp Carbon.adapter

Check environment variables:

echo $SMTP_HOST
echo $SMTP_USERNAME

Enable debug logging:

Carbon.configure do |settings|
  settings.debug = true
end

Templates Not Found

Verify template paths:

ls -la src/mailers/templates/user/

Async Delivery Not Working

Ensure JoobQ workers are running:

azu jobs:worker

Check job queue:

azu jobs:status

Related Documentation

• Carbon Email Documentation

• JoobQ Background Jobs

• Email Best Practices

See Also

• azu generate job - Generate background jobs

• azu jobs:worker - Run job workers

• Email Templates Guide