Project •

💌 Multi SMTP Plus: Unlimited Emails, $0 Spent

Revived an 11-year-old Rails multi-SMTP gem and added round-robin delivery to spread load across free tiers.

👉 Solopreneur update

  • 🔧 Updated an 11-year-old multi-SMTP gem to work with modern Rails
  • 🔄 Added a new round robin mode to distribute load evenly
  • 💸 Result: Unlimited emails, zero dollars spent

🪦 Old but not dead

I found an old gem called multi_smtp. Last update? 2014.

It worked… kinda. But only on old Rails versions. And it lacked something I really needed: a way to spread email load across multiple providers.

Why? Because free tiers exist. And if you rotate them properly, you can send a lot of emails without ever pulling out your credit card.

🧙 The GPT-5 hack

I’ll be honest: I didn’t want to read 11 years of outdated Ruby code.

So I asked GPT-5 to help me upgrade it.

  • Updated it for Rails 8 (works cleanly now)
  • Added round robin delivery: Active loop through every provider you configure, distributing the load evenly

Now you can stack Gmail, Resend, SendGrid, Mailgun—whatever free tiers you have. Emails spread out, limits avoided.

Unlimited emails. $0 spent. 💸📧🤖

⚙️ How it works

  1. List your SMTP providers
  2. Choose round_robin as the delivery mode
  3. Every email cycles to the next provider automatically

📦 Try it

Code’s here: github.com/woosunwoo/multi_smtp

Works out of the box with Rails 8. Perfect for side projects, newsletters, or anyone tired of paying just to send “Welcome” emails.