MailCapture

Catch emails locally while developing, then read them in a browser.

MailCapture is a Go app that gives you:

an SMTP endpoint your app can send emails to
a simple inbox UI to view received messages
raw message view for debugging templates and headers
JSON API endpoints for CI/integration tests

Perfect for local development and demos where you want to verify outgoing emails without sending anything to real users.

Quick Start

Run the app:

go run github.com/nasermirzaei89/mailcapture@latest --smtp-addr :1025 --http-addr :8080

Open the inbox:

http://localhost:8080

Point your app's SMTP settings to:

Host: localhost
Port: 1025
Username/Password: not required

Once your app sends an email, it will appear in the inbox.

What You Can Do

See all captured emails in one place
Open each message to inspect subject, sender, recipients, and body
View raw source to debug headers and MIME output
Catch multiple recipients in a single message
Manage captured messages over HTTP API

Runtime Limits

MailCapture now supports practical in-memory and SMTP limits:

--max-message-bytes (default: 10485760) limits SMTP DATA size per message
--max-recipients (default: 100) limits RCPT TO count per message
--max-messages (default: 1000) caps retained messages in memory (oldest are evicted)

Set any of these to 0 to disable the specific limit.

STARTTLS and AUTH

MailCapture can optionally support TLS upgrade and SMTP authentication:

--smtp-tls-cert-file + --smtp-tls-key-file enable STARTTLS
--smtp-auth-username + --smtp-auth-password enable AUTH PLAIN and AUTH LOGIN
--require-auth requires successful AUTH before MAIL FROM
--allow-insecure-auth allows AUTH before TLS (development only)

When TLS is enabled and insecure auth is not allowed, AUTH is advertised after STARTTLS.

HTTP API

In addition to the HTML UI, these endpoints are available:

GET /healthz returns ok
GET /api/messages returns { "count": n, "messages": [...] }
GET /api/messages/{id} returns one message JSON object
DELETE /api/messages/{id} deletes one message
DELETE /api/messages deletes all messages

Send a Quick Test Email

If you want to test immediately from terminal:

nc -C localhost 1025 <<'EOF'
HELO localhost
MAIL FROM:<from@example.com>
RCPT TO:<to@example.com>
DATA
Subject: Test email
From: from@example.com
To: to@example.com

Hello from MailCapture test.
.
QUIT
EOF

Refresh http://localhost:8080 and you should see the message.

Notes

Emails are stored in memory only
Restarting the app clears all captured messages
Designed for local/dev usage only
Not intended for production use or security-sensitive environments

nasermirzaei89/mailcapture