Introduction

Sending high-volume emails efficiently is crucial for scalability, performance, and deliverability. Rails’ ActionMailer is a powerful tool, but handling thousands or millions of emails requires optimization to avoid performance bottlenecks and delivery failures.

In this guide, we will cover:

✔️ Configuring ActionMailer for optimal performance
✔️ Using background jobs for email processing
✔️ Avoiding spam filters and improving deliverability
✔️ Monitoring email performance with logging and analytics

1. Optimizing ActionMailer Configuration

Choosing the Right Delivery Method

Rails supports multiple email delivery methods, including:

  • :smtp – Best for production with third-party services like SendGrid, Postmark, SES
  • :sendmail – Fast for internal mail servers
  • :test – Useful for development and testing

Configure config/environments/production.rb for SMTP:

config.action_mailer.delivery_method = :smtp  
config.action_mailer.smtp_settings = {  
address: "smtp.sendgrid.net",  
port: 587,  
domain: "yourdomain.com",  
user_name: ENV["SMTP_USERNAME"],  
password: ENV["SMTP_PASSWORD"],  
authentication: "plain",  
enable_starttls_auto: true  
}

✅ Why? Ensures secure, authenticated, and scalable email delivery.

2. Offloading Email Sending to Background Jobs

Sending emails synchronously slows down the application, especially under high load.

Using ActiveJob for Background Email Delivery

Modify your mailer:

class UserMailer < ApplicationMailer  
def welcome_email(user)  
@user = user  
mail(to: @user.email, subject: "Welcome to Our Platform!")  
end  
end

Call it using ActiveJob in the controller:

UserMailer.welcome_email(@user).deliver_later

🚀 Why? deliver_later queues the email, ensuring non-blocking performance.

Configuring Sidekiq for Better Performance

For high-volume email processing, use Sidekiq instead of the default job queue.

Add Sidekiq to Gemfile:

gem "sidekiq"

Configure config/application.rb:

config.active_job.queue_adapter = :sidekiq

✅ Why? Sidekiq uses Redis for faster job execution and better reliability.

3. Enhancing Email Deliverability

Adding SPF, DKIM, and DMARC Records

To avoid spam filters, configure:

  • SPF (Sender Policy Framework) – Prevents spoofing.
  • DKIM (DomainKeys Identified Mail) – Authenticates email origin.
  • DMARC (Domain-based Message Authentication) – Prevents phishing attacks.

Set up SPF in DNS TXT records:

v=spf1 include:sendgrid.net ~all

✅ Why? Helps email providers trust your emails, improving inbox placement.

Using Dedicated IPs for Large Volume Sending

Email providers may throttle bulk emails from shared IPs.

  • Dedicated IP reduces rate limiting.
  • IP warming helps gain reputation gradually.

🚀 Use dedicated IPs for transactional and marketing emails separately.

4. Monitoring and Logging Email Performance

Logging Email Activity

Enable logging to track email issues:

config.action_mailer.logger = Logger.new(STDOUT)  
config.action_mailer.raise_delivery_errors = true

✅ Why? Helps debug delivery failures in production.

Using Third-Party Analytics

SendGrid & Postmark provide analytics for:

  • Open and click rates
  • Bounce and spam complaints
  • Delivery success tracking

🚀 Integrate webhooks for real-time email tracking.

5. Sending Bulk Emails Efficiently

Using Batch Jobs for Bulk Emails

For large email campaigns, send in batches to avoid server overload.

Example using Sidekiq Batches:

class BulkEmailJob  
include Sidekiq::Worker

def perform(batch_id, user_ids)  
users = User.where(id: user_ids)  
users.each do |user|  
UserMailer.newsletter(user).deliver_later  
end  
end  
end

🚀 Why? Reduces the risk of timeouts and rate limiting.

6. Handling Email Failures Gracefully

Retrying Failed Emails

Sidekiq automatically retries failed jobs, but you can customize it:

class TransactionalEmailJob  
include Sidekiq::Worker  
sidekiq_options retry: 5

def perform(user_id)  
user = User.find(user_id)  
UserMailer.transactional_email(user).deliver_now  
rescue StandardError => e  
Rails.logger.error("Email failed: #{e.message}")  
end  
end

🚀 Why? Ensures temporary failures don’t cause permanent data loss.

Fallback for Critical Emails

Use database storage for transactional emails in case of failure:

class UserMailer < ApplicationMailer  
def order_confirmation(user, order)  
@user = user  
@order = order

    begin  
      mail(to: @user.email, subject: "Your Order Confirmation")  
    rescue StandardError  
      EmailLog.create(user_id: @user.id, subject: "Order Confirmation", status: "failed")  
    end  
end  
end

🚀 Why? Logs failed emails for manual retry or recovery.

Conclusion

🚀 Key Takeaways:
✔️ Configure SMTP settings for optimal performance.
✔️ Use background jobs (Sidekiq, ActiveJob) for high-volume email processing.
✔️ Improve deliverability using SPF, DKIM, DMARC, and dedicated IPs.
✔️ Monitor logs, analytics, and email performance.
✔️ Use batch jobs for bulk emails to avoid rate limiting.
✔️ Implement failover mechanisms to ensure critical emails are always sent.

🔗 Next Steps: Implement Rails Mail Preview to test and optimize emails before sending!