MailCatcher
MailCatcher is a free, open-source tool for inspecting email that an application sends during development.
What MailCatcher is
MailCatcher is a free, open-source tool for inspecting email that an application sends during development. It runs a local SMTP server, captures messages and displays them in a web interface. When available, a message can be viewed as HTML, plain text or source. For HTML, MailCatcher adjusts the content so embedded images display and links open in a new window. It lists attachments, supports downloading individual message parts and can provide the original email. New messages appear instantly in browsers with WebSockets support; otherwise, the interface refreshes every thirty seconds.
Its URL API provides message lists and metadata in JSON, along with message content, attachment parts and full source. Setup examples are documented for Rails, PHP and Django. Installation options include a Ruby gem and Docker image. MailCatcher requires Ruby 3.3 or newer, and dependencies may require build tools. Its mail processing is basic, and UTF-8 sent directly over the wire is not completely supported; the maker advises using a mail library that encodes to the SMTP server’s capabilities.
Good
- Free and open source under the MIT License
- Shows HTML, plain text and source when available
- Downloads attachments, message parts and original email
- URL API exposes message data and content
- Setup examples cover Rails, PHP and Django
Watch out
- Requires Ruby 3.3 or newer
- Dependencies may require build tools
- UTF-8 support over the wire is incomplete
- Browsers without WebSockets refresh every thirty seconds
Who it suits
MailCatcher suits developers who want to route an application's email to a local endpoint for inspection during development. It is available for Linux, macOS, web, API and self-hosted use.
Verdict
MailCatcher brings local email capture, message inspection and downloads together with an API. Its basic processing and incomplete direct UTF-8 support are important limits to consider.
The facts
Each one read from MailCatcher's own pages, with the date it was checked.
What it does
- API
- Its REST-style endpoints provide message lists and metadata in JSON, message content, attachments, and full source.checked 10 Oct 2026
- Attachments
- It lists attachments and allows individual parts to be downloaded.checked 10 Oct 2026
- HTML preview
- It rewrites HTML to display embedded images and opens links in a new window.checked 10 Oct 2026
- Images and links
- It rewrites HTML to display embedded images and open links in a new window.checked 4 Oct 2026
- Installation
- The site instructs users to install MailCatcher with `gem install mailcatcher` and run it locally.checked 10 Oct 2026
- Integrations
- The site gives setup instructions for Rails, PHP, and Django applications.checked 10 Oct 2026
- Intended use
- The setup instructions direct applications to send mail to a local SMTP endpoint for inspection in development.checked 4 Oct 2026
- License
- The project is released under the MIT License.checked 10 Oct 2026
- Limitation
- MailCatcher does not completely support UTF-8 sent directly over the wire and advises using a mail library that encodes according to SMTP server capabilities.checked 10 Oct 2026
- Limits
- The maker says mail processing is basic and that UTF-8 is not completely supported directly over the wire.checked 4 Oct 2026
- Live updates
- Messages appear instantly in browsers supporting WebSockets; otherwise, the interface updates every thirty seconds.checked 10 Oct 2026
- Message views
- It shows HTML, plain text, and source versions of messages when available.checked 10 Oct 2026
- Purpose
- MailCatcher runs an SMTP server that catches messages and displays them in a web interface.checked 10 Oct 2026
- Requirements
- The repository README says MailCatcher requires Ruby 3.3 or newer and notes build tools may be needed for dependencies.checked 4 Oct 2026
- Support
- The maker asks users to file an issue and include the complete message when reporting processing problems.checked 10 Oct 2026
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