Background email delivery in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when you call deliver_later on a mailer?

In Rails, when you use deliver_later on a mailer method, what is the expected behavior?

Ruby on Rails

UserMailer.welcome_email(user).deliver_later

A The email is queued to be sent asynchronously by an Active Job worker.

B The email is sent immediately and the method blocks until delivery finishes.

C The email is saved to the database but never sent automatically.

D The email is sent synchronously but only if the server is in development mode.

💡 Hint

Think about how Rails handles background jobs for emails.

Using deliver_later queues the email to be sent asynchronously using Active Job, so the request is not blocked.

📝 Syntax

intermediate

Identify the correct way to enqueue a mailer with arguments

Which of the following is the correct syntax to send a welcome email asynchronously with a user argument?

A UserMailer.deliver_later.welcome_email(user)

B UserMailer.welcome_email(user).deliver_later()

C UserMailer.welcome_email.deliver_later(user)

D UserMailer.welcome_email(user).deliver_now_later

💡 Hint

Remember the order: call mailer method first, then deliver_later.

You call the mailer method with arguments first, then chain deliver_later to enqueue the email.

🔧 Debug

advanced

Why does the email never get sent when using deliver_later?

You have this code in your controller:
UserMailer.welcome_email(@user).deliver_later
But no emails are sent and no errors appear. What is the most likely cause?

A The Active Job queue adapter is set to :test, so jobs are not executed automatically.

B The Active Job queue adapter is set to :inline, so emails are sent immediately.

C The mailer method is missing the <code>mail</code> call inside it.

D The SMTP settings are incorrect, causing silent failures.

💡 Hint

Check your Active Job queue adapter in the environment config.

When the queue adapter is :test, jobs are enqueued but not run automatically, so emails are not sent.

🧠 Conceptual

advanced

What is the benefit of using deliver_later over deliver_now?

Why should you prefer deliver_later instead of deliver_now in a web request?

A deliver_later sends emails synchronously, ensuring immediate delivery.

B deliver_later disables email sending in production to save resources.

C deliver_later stores emails in the database for manual sending later.

D deliver_later queues emails to avoid blocking the web request, improving user experience.

💡 Hint

Think about how web requests should avoid waiting on slow tasks.

deliver_later queues the email to be sent asynchronously, so the user does not wait for the email to send.

❓ state_output

expert

What is the state of the job queue after calling deliver_later once?

Given this code:
UserMailer.notification_email(user).deliver_later
Assuming the queue adapter is :async and no other jobs are running, what is the state of the job queue immediately after this call?

A The job queue is empty because the email is sent immediately.

B The job queue contains one job, but it is delayed by default for 5 minutes.

C The job queue contains one enqueued mail delivery job ready to be processed.

D The job queue contains multiple jobs because deliver_later splits the email into parts.

💡 Hint

deliver_later enqueues exactly one job for the email delivery.

deliver_later enqueues a single job immediately to send the email asynchronously.