Background email delivery in Ruby on Rails - Performance & Optimization

Performance: Background email delivery

HIGH IMPACT

This affects page load speed and user interaction responsiveness by offloading email sending from the main request cycle.

Sending emails after user actions without blocking the UI

Ruby on Rails

def create
  UserMailer.welcome_email(@user).deliver_later
  redirect_to root_path
end

Email is queued and sent asynchronously, freeing the web request to complete immediately.

📈 Performance GainNon-blocking request, improves INP by hundreds of milliseconds

Sending emails after user actions without blocking the UI

Ruby on Rails

def create
  UserMailer.welcome_email(@user).deliver_now
  redirect_to root_path
end

Sending email synchronously blocks the web request until the email is sent, causing slow response times.

📉 Performance CostBlocks rendering for 500ms+ depending on email server response

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Synchronous email sending (deliver_now)	N/A	N/A	Blocks response, delays paint	[X] Bad
Asynchronous email sending (deliver_later)	N/A	N/A	Non-blocking, fast paint	[OK] Good

Rendering Pipeline

Synchronous email sending blocks the main thread during the request, delaying response and paint. Background delivery moves email sending to a separate job queue, allowing the browser to receive and render the page faster.

→Request Handling

→Response Time

→Interaction Responsiveness

⚠️ BottleneckRequest Handling blocking on email delivery

Core Web Vital Affected

INP

This affects page load speed and user interaction responsiveness by offloading email sending from the main request cycle.

Optimization Tips

1Never send emails synchronously during web requests.

2Use deliver_later with a background job processor like Sidekiq or Delayed Job.

3Monitor background job queues to ensure timely email delivery.

Performance Quiz - 3 Questions

What is the main performance problem with sending emails synchronously during a web request?

A It causes layout shifts on the page

B It increases CSS paint time

C It blocks the request, delaying page load and interaction

D It reduces image loading speed

DevTools: Performance

How to check: Record a performance profile while triggering the email sending action. Look for long tasks blocking the main thread during the request.

What to look for: Long blocking tasks or delayed Time to Interactive indicate synchronous email sending.