Background email delivery in Ruby on Rails - Step-by-Step Execution

Concept Flow - Background email delivery

User triggers email send

↓

Create email job

↓

Add job to queue

↓

Background worker picks job

↓

Send email asynchronously

↓

Job completes, user continues

This flow shows how an email send request is turned into a background job, queued, and processed asynchronously so the user doesn't wait.

Execution Sample

Ruby on Rails

class UserMailer < ApplicationMailer
  def welcome_email(user)
    mail(to: user.email, subject: 'Welcome!')
  end
end

UserMailer.with(user: @user).welcome_email.deliver_later

This code defines an email and sends it in the background using deliver_later.

Execution Table

Step	Action	Evaluation	Result
1	Call deliver_later on welcome_email	Creates a job to send email	Job added to queue
2	Background worker picks job	Starts executing email send	Email sending begins
3	Mail method builds email content	Email content ready	Email ready to send
4	Email sent via SMTP or service	Email delivered	User receives email
5	Job marked complete	Worker ready for next job	Background process idle
6	User continues without waiting	No delay in user flow	Smooth user experience

💡 Job completes after email is sent, user flow is not blocked by email delivery

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
job_status	none	queued	processing	building email	sent	completed
user_flow	waiting	continued	continued	continued	continued	continued

Key Moments - 3 Insights

Why doesn't the user wait for the email to send?

Because deliver_later creates a background job (see execution_table step 1) that runs separately, so the user flow continues immediately (step 6).

What happens if the background worker is busy?

The job stays queued until a worker is free (job_status stays 'queued' in variable_tracker), so email sending is delayed but user flow is unaffected.

How does Rails know what email to send in the background?

The mail method builds the email content inside the job (step 3), so the job has all info needed to send the email asynchronously.

Visual Quiz - 3 Questions

Look at the execution_table, what is the job_status after step 2?

A queued

B sent

C processing

D completed

💡 Hint

Check variable_tracker row for job_status after Step 2

At which step does the user flow continue without waiting?

A Step 3

B Step 6

C Step 1

D Step 4

💡 Hint

Look at execution_table step describing user continuing

If deliver_now was used instead of deliver_later, how would the execution_table change?

A User would wait until email is sent

B Job would be queued but not processed

C Background worker picks job immediately

D Email would never be sent

💡 Hint

deliver_now sends email immediately blocking user flow, unlike deliver_later

Concept Snapshot

Background email delivery in Rails:
- Use deliver_later to send emails asynchronously
- Creates a job added to a queue
- Background worker processes job and sends email
- User flow continues without waiting
- Improves app responsiveness and user experience

Full Transcript

Background email delivery in Rails works by turning an email send request into a background job using deliver_later. This job is added to a queue and processed by a background worker separately from the user's request. The worker builds the email content and sends it asynchronously. This means the user does not wait for the email to send and experiences a smooth flow. The job status changes from queued to processing to completed as the email is sent. If deliver_now is used instead, the user waits for the email to send, blocking the flow. Using background jobs improves app performance and user satisfaction.