#email-template #open #source #host #yourself #destination #quickly

app catapulte

Catapulte is an open source mailer you can host yourself. You can use it to quickly catapult your transactionnal emails to destination.

2 releases (1 stable)

1.0.0 Mar 5, 2024
1.0.0-alpha-1 Jan 4, 2024

#32 in Email

Download history 12/week @ 2024-01-01 16/week @ 2024-02-19 7/week @ 2024-02-26 153/week @ 2024-03-04 16/week @ 2024-03-11 5/week @ 2024-03-18 58/week @ 2024-04-01

84 downloads per month

Custom license



Build Status codecov

Docker Pulls Docker Image Size (latest by date)

What is catapulte?

Catapulte is an open source mailer you can host yourself.

You can use it to quickly catapult your transactionnal emails to destination.


Why did we build catapulte?

Catapulte comes from the frustration of using several email providers. We used to work with products like sendgrid, mailgun, mailchimp, sendinblue, etc.

But they have many disadvantages :

  • Most of them are not really transactionnal oriented, and users complain that their login emails take a long time to arrive.
  • You cannot host it nor use it on premise
  • It's American, with the patriot act, they are able to access your users data.
  • They usually don't have templating tools for our non tech coworkers that ask us to change a wording every 2 days. And when they do, the editors are like html online editors, so it ends up being our job to make the template anyway.

How to use it?

Catapulte is a simple service that renders your mjml template, interpolates the data and then sends it to a SMTP server. If you want to see how to create your own template, take a look at the /template folder in this repository.

You then have several options for starting catapulte. We recommend using Docker if you are on a amd64, i386 or arm64v8 architecture. By doing the following, you'll be able to have a running server that will render and send your email.

docker run -d \
  --name catapulte \
  -e SMTP__HOSTNAME=localhost \
  -e SMTP__PORT=25 \
  -e SMTP__USERNAME=optional \
  -e SMTP__PASSWORD=optional \
  -e SMTP__TLS_ENABLED=true \
  -e TEMPLATE__TYPE=local \
  -e TEMPLATE__PATH=/templates \
  -p 3000:3000 \
  -v /path/to/your/templates:/templates:ro \

Once your server started, you can simply send an email using an HTTP request.

curl -X POST -v \
  -H "Content-Type: application/json" \
  --data '{"from":"alice@example.com","to":"bob@example.com","params":{"some":"data"}}' \

You can also send attachments using a multipart request.

curl -X POST -v \
  -F attachments=@asset/cat.jpg \
  -F from=alice@example.com \
  -F to=bob@example.com \
  -F params='{"some":"data"}' \

You can configure it with some environment variable and can find more information in this wiki.

If you some API specification, the Open API specification is also available on /openapi.json when Catapulte is running.

To use it in production, we prepared a documentation on how to use Catapulte with Amazon Simple Email Service.

Sending to multiple recipients

You can send the same email to multiple recipients just by using an array in the to field, like this:

curl -X POST -v \
  -H "Content-Type: application/json" \
  --data '{"from":"alice@example.com","to":["bob@example.com","jon@example.com"],"params":{"some":"data"}}' \

Should you use it?

If, like us, you didn't find any good way of doing transactionnal emails, then YES!

Why you should use it :

  • You work in a startup

    • You don't have shit loads of money to spend on the mailing tools, so use something opensource, send your emails from your own SMTP (or from Amazon SES, it's cheap)
    • You don't have time to change the email template everyday, so let your Product Owner do it
    • You wanna be able to add this little feature, just do a pull request...
  • You work in a big company

    • You cannot use those external services because you're not allowed to put your user's data on an external service.
    • You cannot access external services because it's blocked by the proxy
    • You want to customise the way you authenticate to your SMTP
    • You want something user friendly enough that your manager can write the emails

Thank you!

Buy Me A Coffee


~1M SLoC