Free · Open source · Self-hosted
sendthen is an open-source alternative to email services like Resend — except it runs on your server. Send email from your app with one API call, write newsletters, receive replies, and watch every delivery. All from a single Docker container.
import { SendThen } from 'sendthen';
const st = new SendThen('st_xxxxxxxx');
await st.emails.send({
from: 'you <hello@yourdomain.com>',
to: 'user@example.com',
subject: 'Welcome aboard',
html: '<strong>It just sends.</strong>',
});This is the whole integration — one request. Copy it, change the domain, and you’re sending.
How it works
No accounts to create with anyone, no sales calls, no plans to pick. You run it, you connect a domain, you send.
Start sendthen on any server with Docker. The app, the database, and the sending queue all live inside one container — there is nothing else to set up.
docker compose up -dAdd your domain in the dashboard and copy the DNS records it gives you. Once they verify, you can send as anything@yourdomain.com.
TXT stmail._domainkey → verifiedCall the API from any language — or write newsletters and design templates right in the dashboard. Every email shows up with its full delivery story.
POST /api/v1/emails → 200Under the hood
Every email takes the same five steps, and you can watch each one happen in the dashboard or from the CLI.
What you get
Four jobs most products end up paying four different tools for. sendthen does all of them from the same dashboard and API.
The emails your product needs to send — welcomes, receipts, password resets.
Write once and send a personal copy to everyone on a list.
Replies and inbound mail land in the same dashboard you send from.
A visual builder for emails that look right in every mail client.
Why self-host
Every email, contact, and template lives in one SQLite file on your server. Back it up, move it, open it — no vendor holds it for you.
Send through Amazon SES, any SMTP relay, or directly to the recipient’s mail server. Switch later without changing a line of your code.
App emails, newsletters, incoming mail, templates, and analytics share one dashboard — no second service to sign up for.
Compare · checked
This compares how each product is run and operated — not features or deliverability. The managed services are excellent at what they do; they just work differently.
| What we compared | Sendthenthis project | Resend | Postmark | SendGrid | Mailgun |
|---|---|---|---|---|---|
| Runs on your own server | Yes — you host it | Managed service | Managed service | Managed service | Managed service |
| Source code | Open (MIT license) | Managed service | Managed service | Managed service | Managed service |
| How your mail is delivered | You choose: SES, SMTP, or direct | Provider-managed delivery | Provider-managed delivery | Provider-managed delivery | Provider-managed delivery |
| Testing without sending real mail | Built-in sandbox saves emails to disk | Managed test addresses | Managed sandbox server | Managed request validation | Managed test mode |
| Where your data lives | Portable /data volume | Provider-managed state | Provider-managed state | Provider-managed state | Provider-managed state |
| Software cost | None when self-hosted | Managed service plan | Managed service plan | Managed service plan | Managed service plan |
Self-hosting removes Sendthen software usage fees. Infrastructure and delivery-provider charges still apply.
Managed-service cells describe publicly documented offerings checked 2026-07-13; they do not claim that undocumented or private options cannot exist.
Get started
Clone it, start it, open it. It boots in sandbox mode, so you can try the whole thing — sending, tracking, webhooks — before a single real email leaves your machine.
git clone https://github.com/emreisik95/sendthen && cd sendthen
docker compose up -d
# open http://localhost:3000Recommended
Free forever under the MIT license. Your emails, contacts, and settings live in one portable /data folder you can back up or move anywhere.
No server handy?
The same product, running on our servers instead of yours. Handy for trying sendthen before you deploy it.
Try it hostedOne container, three lines in a terminal, and your email stack runs on your terms.