Mail Mantis
GitHub
Free forever · open source · self-hosted

Free, open-source email warm-up you run yourself.

Build your domain’s reputation so your email reaches the inbox, not spam. AI writes everyday emails, Mail Mantis sends them to inboxes you own and keeps the conversations going every day on autopilot, and you see exactly where each one landed. No subscription, no per-inbox fees, and your data stays on your server.

Start free in 3 commandsStar on GitHub
$git clone https://github.com/karuridavid/mailmantis && cd mailmantis && docker compose up -d
Mail Mantis overview: inbox rate, a per-inbox placement grid, items needing attention and recent activity

Free and open source

MIT licensed. No plans, no seat limits, no card. Read every line of the code.

Self-hosted

Runs on your machine, your server or Vercel. Your inboxes and data stay with you.

Real conversations

Two-way threads between your domain and real inboxes, not a pool of strangers’ bots.

Daily autopilot

Switch it on and it sends and replies every day. Pause it with one click.

HOW IT WORKS

From cold domain to trusted sender.

Inbox providers trust domains that send ordinary mail people open and reply to. Mail Mantis creates exactly that, in four steps, and shows you the result for every email.

Connect

Add your domain’s SMTP sender and test it. Connect Gmail, Outlook, Yahoo, iCloud or IMAP inboxes you own, or invite friends to lend theirs.

Brief

AI reads your public website and drafts a business brief. You correct it, or write it yourself.

Draft & send

Get a different, ordinary email for each inbox. Edit, mark ready and send, or let autopilot send a few each day.

Check & converse

See Primary, Promotions or Spam for every send. Reply from the seed inbox, then answer back from your domain in the same thread.

FEATURES

Everything you need to warm up a domain. No monthly bill.

Inbox signal grid

Every seed inbox against its latest sends. Problems stand out at a glance.

Real inbox placement

Gmail tabs, Outlook Focused and Other, and spam folders, read straight from each mailbox.

PrimaryPromotionsSpam

Bring your own AI

Gemini, Claude, OpenAI, OpenRouter, Groq or Cloudflare Workers AI with your own key, or paste the prompt into any chat app. Emails come from a brief you approved, with no invented offers.

Two-way conversations

Reply from the seed inbox, then answer back from your domain, all in the same thread. AI drafts each reply from the conversation so far.

Not spam, important, filters

Move an email out of spam or mark it important when you choose. One click adds a Gmail filter that skips Spam and marks your mail important.

Autopilot

A daily run that sends a few new emails and moves each conversation on by one reply. Choose 1 to 10 emails a day, run it now, or pause it any time.

THE EMAILS VIEW

Every email, from draft to reply.

A mail-client layout with colour-coded status. Open any email to edit it, send it, see its placement and timeline, or continue the conversation.

  • Draft → Ready → Sent, with a confirmation before anything leaves
  • Placement checked automatically while the dashboard is open, with a clear warning when an email never arrived
  • Replies from the seed and from your domain, threaded together
  • Keyboard friendly: J/K to move, N for new emails
  • Several sender domains, one warmed at a time
  • Light and dark themes, and installable as an app
Emails view: list of emails with status pills and an open email showing its placement in the Primary inbox, a timeline and a reply
~/mailmantis
$ git clone https://github.com/karuridavid/mailmantis
$ cd mailmantis && docker compose up -d
$ docker compose logs app | grep "setup key"
# First sign-in: open the dashboard and use this
# one-time setup key: 9xQ…
# → http://localhost:8080
SELF-HOST

Free to run. Up in three commands.

Docker Compose starts Postgres and the app, generates the encryption key on first boot, and runs autopilot’s daily schedule itself. Add HTTPS for a public domain with one more flag, or deploy to Vercel with Neon.

Read the guideTech stack
WHY MAIL MANTIS

Warm-up without the subscription or the black box.

Most warm-up services charge every month, often per inbox, and swap mail with a shared pool of other customers’ inboxes. Mail Mantis works differently.

Mail MantisTypical warm-up service
PriceFree, foreverMonthly subscription, often per inbox
Who your mail talks toYour own inboxes and friends’, in real threadsA shared pool of strangers’ inboxes
What you seePrimary, Promotions or Spam for every single emailOften a single health score
AI writingSix AI services, your own key, several with free tiersTheir templates or their AI
Your data and keysOn your server, encrypted at restOn their servers
Source codeOpen, MIT licensedClosed

For your own domains and inboxes

Mail Mantis sends a handful of emails a day, only to inboxes you own or that friends lend you. It is not a bulk sender or an outreach tool, and it can’t guarantee inbox placement. Good authentication (SPF, DKIM, DMARC) and real engagement matter far more than any tool.

Start warming up your domain today.

Free and open source under the MIT license. No account, no card, no limit on inboxes.

Get started freeStar on GitHub