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sj26/mailcatcher

A local SMTP server that catches outgoing email during development and shows it in a web interface.

Open-source alternative to:Mailtrap

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What is it?

MailCatcher runs a simple SMTP server that catches every message sent to it and displays them in a web interface. You point your application's mail delivery at smtp://127.0.0.1:1025 instead of a real mail server, then open http://127.0.0.1:1080 to browse the messages that have arrived. It is aimed at developers who need to test outgoing email without delivering it to real recipients.

Messages can be viewed as HTML, plain text, or source. HTML is rewritten so embedded images display and links open in a new window. Attachments can be listed and downloaded individually, and the original email can be exported to open in a native mail client. A JSON and HTTP API exposes the message list and parts.

MailCatcher is installed as a Ruby gem and requires Ruby 3.3 or newer. Ports and IPs can be changed from the command line, and an official Docker image is available. Integration guidance is included for Rails, Django, and PHP through a sendmail-compatible `catchmail` command.

Key features

  • 01Catches all outgoing mail and stores it for display in the browser.
  • 02Shows messages as HTML, plain text, or source.
  • 03Lists attachments and allows downloading each part separately.
  • 04Exports the original email for use in a native mail client.
  • 05Updates instantly over WebSockets when supported, otherwise polls periodically.
  • 06Provides a JSON and HTTP API for messages and their parts.

Use cases

  • Testing password reset, signup, and notification emails during local development.
  • Checking email output from Rails, Django, or PHP applications without sending real mail.
  • Running a disposable mail catcher in Docker for CI or demo environments.

Quick start

  1. 1

    Install MailCatcher with RubyGems

    gem install mailcatcher
  2. 2

    Start MailCatcher

    mailcatcher
  3. 3

    Open the web interface at http://127.0.0.1:1080/ and send mail via smtp://127.0.0.1:1025

Things to know

  • Requires Ruby 3.3 or newer, and some gem dependencies may need build tools.

In collections

Testing frameworks & test automation tools

Topics

#smtp#email#testing#ruby#development-tools#local-development#docker#development#devtools#mail

FAQ

What is mailcatcher?
A local SMTP server that catches outgoing email during development and shows it in a web interface. MailCatcher runs a simple SMTP server that catches every message sent to it and displays them in a web interface. You point your application's mail delivery at smtp://127.0.0.1:1025 instead of a real mail server, then open http://127.0.0.1:1080 to browse the messages that have arrived. It is aimed at developers who need to test outgoing email without delivering it to real recipients.
Is mailcatcher free to use? What license does it have?
mailcatcher is open source under the MIT license. Check the license terms before using it in commercial products.
Is mailcatcher still maintained?
Updated within 6 months. The last commit to mailcatcher was on Sep 16, 2026.
What can I use mailcatcher for?
Testing password reset, signup, and notification emails during local development. Checking email output from Rails, Django, or PHP applications without sending real mail. Running a disposable mail catcher in Docker for CI or demo environments.
How do I install mailcatcher?
Install MailCatcher with RubyGems: gem install mailcatcher Start MailCatcher: mailcatcher Open the web interface at http://127.0.0.1:1080/ and send mail via smtp://127.0.0.1:1025
Where can I get mailcatcher?
The source code and installation instructions are on GitHub: https://github.com/sj26/mailcatcher

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