Email Warmup System

Self-hosted email warmup with AI-written conversations. $0 a month.

Self-hosted web app
TypeScript
Active
Personal project

The problem I faced

New domains for client cold outreach kept landing in spam, and warmup SaaS cost me more than $40 a month per mailbox, with no visibility into what the shared network was doing to my senders.

What I built

A self-hosted warmup system that sends AI-written emails between my own mailboxes, opens and replies like a person, rescues mail from spam, and pauses automatically if anything looks unsafe.

The problem

New or freshly parked domains have no reputation, so mailbox providers send their mail to spam or throttle it. The usual fix is a warmup service, but they charge per mailbox every month and put your mailboxes in a shared network you can’t see into.

I was paying more than $40 a month per mailbox for client outreach domains, and still couldn’t tell what the network was doing.

What I built

A warmup system I host myself:

AI-written conversations. Every subject and body is generated fresh, so providers can’t fingerprint repeated templates. Replies actually respond to the previous email.
Ramp plans of 7, 14 or 30 days, with the day-by-day volume shown before you start.
Human-like behaviour: sends at random times within business hours, opens mail, marks some as important, replies after a delay and moves mail out of spam.
Safety first: the ramp pauses automatically if the bounce rate goes above 2% or spam rescues rise above 30%.
A real dashboard with every send, open, reply, rescue and bounce, plus an SPF, DKIM and DMARC checker.

The result

After running the 14-day plan on a fresh domain, cold outreach that used to land in spam started reaching the inbox. It now runs in maintenance mode in the background.

How it’s built

A Next.js 14 dashboard with API routes and serverless cron, TypeScript end to end, and Prisma with PostgreSQL (or SQLite locally). Nodemailer sends, IMAPFlow reads, and mailbox passwords are encrypted with AES-256-GCM.

Built with AI

The deliverability logic and safety rules came from my own outreach experience. Claude, Codex and Cursor helped me build it quickly and carefully.

Frequently asked questions

Is the email warmup system free?

Yes. It is open source under the MIT license. With free hosting mailboxes and a free OpenRouter model it runs at $0 a month.

How is it different from warmup tools like Instantly or Warmbox?

Your mailboxes only talk to each other instead of joining a shared network, every email is generated fresh by AI, and the dashboard shows every send, open, reply and rescue.