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MailDev is sponsored by ⭐️ inngest/inngest. Inngest is an open-source, event-driven platform that makes it easy for developers to build, test and deploy serverless functions that are triggered by events. Check it out and give it a star!

MailDev is a simple way to test your project's generated email during development, with an easy to use web interface that runs on your machine built on top of Node.js.

MailDev Screenshot

Docker Run

If you want to use MailDev with Docker, you can use the maildev/maildev image on Docker Hub. For a guide for usage with Docker, checkout the docs.

$ docker run -p 1080:1080 -p 1025:1025 maildev/maildev


Usage: maildev [options]
Options Environment variable Description
-s, --smtp <port> MAILDEV_SMTP_PORT SMTP port to catch mail
-w, --web <port> MAILDEV_WEB_PORT Port to run the Web GUI
--mail-directory <path> MAILDEV_MAIL_DIRECTORY Directory for persisting mail
--https MAILDEV_HTTPS Switch from http to https protocol
--https-key <file> MAILDEV_HTTPS_KEY The file path to the ssl private key
--https-cert <file> MAILDEV_HTTPS_CERT The file path to the ssl cert file
--ip <ip address> MAILDEV_IP IP Address to bind SMTP service to
--outgoing-host <host> MAILDEV_OUTGOING_HOST SMTP host for outgoing mail
--outgoing-port <port> MAILDEV_OUTGOING_PORT SMTP port for outgoing mail
--outgoing-user <user> MAILDEV_OUTGOING_USER SMTP user for outgoing mail
--outgoing-pass <password> MAILDEV_OUTGOING_PASS SMTP password for outgoing mail
--outgoing-secure MAILDEV_OUTGOING_SECURE Use SMTP SSL for outgoing mail
--auto-relay [email] MAILDEV_AUTO_RELAY Use auto-relay mode. Optional relay email address
--auto-relay-rules <file> MAILDEV_AUTO_RELAY_RULES Filter rules for auto relay mode
--incoming-user <user> MAILDEV_INCOMING_USER SMTP user for incoming mail
--incoming-pass <pass> MAILDEV_INCOMING_PASS SMTP password for incoming mail
--incoming-secure MAILDEV_INCOMING_SECURE Use SMTP SSL for incoming emails
--incoming-cert <path> MAILDEV_INCOMING_CERT Cert file location for incoming SSL
--incoming-key <path> MAILDEV_INCOMING_KEY Key file location for incoming SSL
--web-ip <ip address> MAILDEV_WEB_IP IP Address to bind HTTP service to, defaults to --ip
--web-user <user> MAILDEV_WEB_USER HTTP user for GUI
--web-pass <password> MAILDEV_WEB_PASS HTTP password for GUI
--base-pathname <path> MAILDEV_BASE_PATHNAME Base path for URLs
--disable-web MAILDEV_DISABLE_WEB Disable the use of the web interface. Useful for unit testing
--hide-extensions <extensions> MAILDEV_HIDE_EXTENSIONS Comma separated list of SMTP extensions to NOT advertise (SMTPUTF8, PIPELINING, 8BITMIME)
-o, --open Open the Web GUI after startup
-v, --verbose
--log-mail-contents Log a JSON representation of each incoming mail


MailDev can be used in your Node.js application. For more info view the API docs.

const MailDev = require("maildev");

const maildev = new MailDev();


maildev.on("new", function (email) {
  // We got a new email!

MailDev also has a REST API. For more info view the docs.

Outgoing email

Maildev optionally supports selectively relaying email to an outgoing SMTP server. If you configure outgoing email with the --outgoing-* options you can click "Relay" on an individual email to relay through MailDev out to a real SMTP service that will *actually* send the email to the recipient.


$ maildev --outgoing-host \
          --outgoing-secure \
          --outgoing-user '' \
          --outgoing-pass '<pass>'

Auto relay mode

Enabling the auto relay mode will automatically send each email to it's recipient without the need to click the "Relay" button mentioned above. The outgoing email options are required to enable this feature.

Optionally you may pass an single email address which Maildev will forward all emails to instead of the original recipient. For example, using --auto-relay will forward all emails to that address automatically.

Additionally, you can pass a valid json file with additional configuration for what email addresses you would like to allow or deny. The last matching rule in the array will be the rule MailDev will follow.


$ maildev --outgoing-host \
          --outgoing-secure \
          --outgoing-user '' \
          --outgoing-pass '<pass>' \
          --auto-relay \
          --auto-relay-rules file.json

Rules example file:

  { "allow": "*" },
  { "deny": "*" },
  { "allow": "" },
  { "deny": "*" },
  { "allow": "" }

This would allow,,, but deny

Configure your project

Configure your application to send emails via port 1025 and open localhost:1080 in your browser.

Nodemailer (v1.0+)

// We add this setting to tell nodemailer the host isn't secure during dev

const transport = nodemailer.createTransport({
  port: 1025,
  // other settings...

Django -- Add EMAIL_PORT = 1025 in your settings file [source]

Rails -- config settings:

config.action_mailer.delivery_method = :smtp
    config.action_mailer.smtp_settings = {
        address: "localhost",
        port: 1025,
        enable_starttls_auto: false

Drupal -- Install and configure SMTP module or use a library like SwiftMailer.


  • Toggle between HTML, plain text views as well as view email headers
  • Test responsive emails with resizable preview pane available for various screen sizes
  • Ability to receive and view email attachments
  • WebSocket integration keeps the interface in sync once emails are received
  • Command line interface for configuring SMTP and web interface ports
  • Ability to relay email to an upstream SMTP server


If you're using MailDev and you have a great idea, I'd love to hear it. If you're not using MailDev because it lacks a feature, I'd love to hear that too. Add an issue to the repo here.


Any help on MailDev would be awesome. There is plenty of room for improvement. Feel free to create a Pull Request from small to big changes.

To run MailDev during development:

npm install
npm run dev

The "dev" task will run MailDev using nodemon and restart automatically when changes are detected. On *.scss file save, the css will also be recompiled. Using test/send.js, a few test emails will be sent every time the application restarts.

If you want to debug you can use the nodemon debug profile in VSCode. To change arguments or environment variables edit the .vscode\launch.json.

The project uses the JavaScript Standard coding style. To lint your code before submitting your PR, run npm run lint.

To run the test suite:

$ npm test



MailDev is built on using great open source projects including Express, AngularJS, Font Awesome and two great projects from Andris Reinman: smtp-server and mailparser. Many thanks to Andris as his projects are the backbone of this app and to MailCatcher for the inspiration.

Additionally, thanks to all the awesome contributors to the project.



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