Action Mailer setup in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when you call deliver_now on a mailer method?

Consider a Rails mailer method that sends an email. What is the behavior when you call deliver_now on the mailer method?

Ruby on Rails

UserMailer.welcome_email(user).deliver_now

A The email is sent immediately during the current request.

B The email is discarded and not sent.

C The email is saved to the database but not sent.

D The email is queued to be sent later by a background job.

💡 Hint

Think about synchronous vs asynchronous email sending.

deliver_now sends the email immediately during the current request cycle, blocking until the email is sent.

📝 Syntax

intermediate

Which option correctly sets the default 'from' email in a mailer class?

In a Rails mailer class, how do you set the default sender email address for all emails?

Ruby on Rails

class UserMailer < ApplicationMailer
  # set default from here
end

A from default: '[e-mail]'

B set_default from: '[e-mail]'

C default_from '[e-mail]'

D default from: '[e-mail]'

💡 Hint

Look for the correct method name and syntax for setting defaults.

The correct syntax is default from: 'email' inside the mailer class.

🔧 Debug

advanced

Why does this mailer method raise an error?

Given the following mailer method, why does calling UserMailer.notify(user).deliver_now raise an error?

Ruby on Rails

class UserMailer < ApplicationMailer
  def notify(user)
    mail(to: user.email, subject: 'Notification') do |format|
      format.text { render plain: 'Hello!' }
      format.html { render html: '<strong>Hello!</strong>'.html_safe }
    end
  end
end

A The block passed to <code>mail</code> is missing a closing <code>end</code>.

B The <code>html_safe</code> method is not allowed inside mailer views.

C The <code>render html:</code> call requires a template, not a string.

D The mailer method is missing a <code>return</code> statement.

💡 Hint

Check how render works inside mailers.

render html: expects a template or partial, not a raw string. To send raw HTML, use format.html { render inline: ... } or format.html { render html: ... } with safe HTML.

❓ state_output

advanced

What is the value of @greeting in the mailer view after calling this method?

Consider this mailer method:

def welcome(user)
  @greeting = "Hello, #{user.name}!"
  mail(to: user.email, subject: 'Welcome')
end

What will @greeting contain in the mailer view?

A The string "Hello, " followed by the user's name and an exclamation mark.

B Nil, because instance variables are not passed to mailer views.

C An empty string, since <code>@greeting</code> is not set in the view.

D The user's email address.

💡 Hint

Think about how instance variables work in mailers and views.

Instance variables set in the mailer method are available in the mailer views, so @greeting will contain the greeting string with the user's name.

🧠 Conceptual

expert

Which configuration is required to send emails asynchronously using Active Job with Action Mailer?

You want to send emails without blocking the web request by using background jobs. Which configuration and method call combination achieves this in Rails?

A Set <code>config.action_mailer.delivery_method = :sendmail</code> and call <code>deliver_now</code> on the mailer method.

B Set <code>config.action_mailer.delivery_method = :smtp</code> and call <code>deliver_later</code> on the mailer method.

C Set <code>config.action_mailer.perform_deliveries = false</code> and call <code>deliver_later</code> on the mailer method.

D Set <code>config.active_job.queue_adapter = :inline</code> and call <code>deliver_now</code> on the mailer method.

💡 Hint

Consider how to enable background job processing and which mailer method triggers async sending.

To send emails asynchronously, you must have a background job adapter configured (like Sidekiq or the default async adapter) and call deliver_later. The delivery method (like SMTP) must be set to actually send emails.

Practice

1. What is the main purpose of Action Mailer in a Rails application?

easy

A. To manage database migrations automatically

B. To send emails by defining mailer classes and methods

C. To handle user authentication and sessions

D. To style HTML views with CSS

Solution

1. Step 1: Understand Action Mailer role

   Action Mailer is designed to send emails by organizing mailer classes and methods.

2. Step 2: Compare with other Rails features

   Database migrations, authentication, and styling are handled by other parts of Rails, not Action Mailer.

3. Final Answer:

   To send emails by defining mailer classes and methods -> Option B

4. Quick Check:

   Action Mailer = send emails [OK]

Hint: Remember: Action Mailer is for emails, not database or styling [OK]

Common Mistakes:

• Confusing Action Mailer with Active Record migrations
• Thinking it handles user login or CSS styling
• Assuming it manages background jobs directly

2. Which of the following is the correct way to define a mailer method in a Rails mailer class?

easy

A. def welcome_email(user) mail to: user.email, subject: 'Welcome' end

B. def welcome_email(user) { send_email(to: user.email) }

C. def welcome_email(user) mail(to user.email, subject 'Welcome') end

D. def welcome_email(user); mail(to: user.email, subject: 'Welcome'); end

Solution

1. Step 1: Check Ruby method syntax

   Method definitions use def name(params); ...; end with parentheses and semicolons optional but recommended for clarity.

2. Step 2: Verify mail method usage

   The mail method requires keyword arguments with colons, e.g., to: user.email, and commas between arguments.

3. Final Answer:

   def welcome_email(user); mail(to: user.email, subject: 'Welcome'); end -> Option D

4. Quick Check:

   Correct Ruby method and mail syntax = def welcome_email(user); mail(to: user.email, subject: 'Welcome'); end [OK]

Hint: Use parentheses and colons for keyword args in mail method [OK]

Common Mistakes:

• Missing parentheses or commas in method definition
• Using braces {} instead of do...end or semicolons
• Omitting colons in keyword arguments

3. Given this mailer method in Rails:

class UserMailer < ApplicationMailer
  def notify(user)
    mail(to: user.email, subject: 'Notice')
  end
end

What will happen when you call UserMailer.notify(user).deliver_now?

medium

A. An email is sent immediately to the user's email address

B. An email is queued but not sent until later

C. A syntax error occurs because deliver_now is invalid

D. Nothing happens because notify method lacks a body

Solution

1. Step 1: Understand deliver_now behavior

   The deliver_now method sends the email immediately when called on a mail object.

2. Step 2: Check mailer method correctness

   The notify method calls mail with valid parameters, so it returns a mail object ready to send.

3. Final Answer:

   An email is sent immediately to the user's email address -> Option A

4. Quick Check:

   deliver_now sends email immediately = An email is sent immediately to the user's email address [OK]

Hint: deliver_now sends email immediately, deliver_later queues it [OK]

Common Mistakes:

• Confusing deliver_now with deliver_later
• Thinking mail method sends email by itself
• Assuming notify method must have email body text

4. You wrote this mailer method:

def alert(user)
  mail(to: user.email, subject: 'Alert')
end

But emails are not sending. Which is the most likely cause?

medium

A. SMTP settings are not configured properly in environment files

B. The mail method is missing a block with email body content

C. You forgot to call deliver_now or deliver_later

D. Mailer class must inherit from ActionMailer::Base explicitly

Solution

1. Step 1: Check SMTP configuration

   Without proper SMTP settings, emails cannot be sent even if mailer code is correct.

2. Step 2: Review other options

   Mailer inheritance from ApplicationMailer is standard; mail method can use templates for body; calling deliver_now is needed but question implies method is called.

3. Final Answer:

   SMTP settings are not configured properly in environment files -> Option A

4. Quick Check:

   SMTP config missing = emails not sent [OK]

Hint: Check SMTP setup first if emails don't send [OK]

Common Mistakes:

• Assuming mail method sends email without deliver_now
• Forgetting to configure SMTP in config/environments
• Thinking mailer must inherit directly from ActionMailer::Base

5. You want to configure Action Mailer to send emails via Gmail SMTP in production. Which configuration snippet in config/environments/production.rb is correct?

hard

A. config.action_mailer.smtp_settings = { address: 'smtp.gmail.com', port: 587, domain: 'gmail.com', user_name: ENV['GMAIL_USERNAME'], password: ENV['GMAIL_PASSWORD'], authentication: 'plain' }

B. config.action_mailer.smtp_settings = { address: 'smtp.gmail.com', port: 25, domain: 'gmail.com', user_name: 'user', password: 'pass', authentication: 'login', enable_ssl: true }

C. config.action_mailer.smtp_settings = { address: 'smtp.gmail.com', port: 587, domain: 'yourdomain.com', user_name: ENV['GMAIL_USERNAME'], password: ENV['GMAIL_PASSWORD'], authentication: 'plain', enable_starttls_auto: true }

D. config.action_mailer.smtp_settings = { address: 'smtp.gmail.com', port: 465, domain: 'yourdomain.com', user_name: ENV['GMAIL_USERNAME'], password: ENV['GMAIL_PASSWORD'], authentication: 'plain', enable_starttls_auto: false }

Solution

1. Step 1: Identify correct SMTP port and security

   Gmail SMTP uses port 587 with STARTTLS enabled (enable_starttls_auto: true) for secure email sending.

2. Step 2: Check domain and authentication

   Domain should be your app's domain, authentication 'plain' is standard, and credentials should come from environment variables for security.

3. Final Answer:

   config.action_mailer.smtp_settings = { address: 'smtp.gmail.com', port: 587, domain: 'yourdomain.com', user_name: ENV['GMAIL_USERNAME'], password: ENV['GMAIL_PASSWORD'], authentication: 'plain', enable_starttls_auto: true } -> Option C

4. Quick Check:

   Gmail SMTP with port 587 and STARTTLS = config.action_mailer.smtp_settings = { address: 'smtp.gmail.com', port: 587, domain: 'yourdomain.com', user_name: ENV['GMAIL_USERNAME'], password: ENV['GMAIL_PASSWORD'], authentication: 'plain', enable_starttls_auto: true } [OK]

Hint: Use port 587 and enable_starttls_auto true for Gmail SMTP [OK]

Common Mistakes:

• Using wrong port like 25 or 465 without proper TLS
• Setting domain to 'gmail.com' instead of your app domain
• Omitting enable_starttls_auto or setting it false