About
Deadletter is a small, self-contained SMTP sink designed for local development and testing. Instead of sending emails to real SMTP providers, applications send them to Deadletter. Every message is captured exactly once as a raw .eml file plus immutable metadata, and indexed in memory so it can be inspected, replayed, and observed through a simple HTTP API or web UI.
The filesystem is the source of truth. In-memory state exists only to support fast inspection, derived metrics, timelines, and replay counters. Deadletter is intentionally minimal: no external dependencies, no fake inboxes, and no risk of accidentally delivering emails to real users.
Features
SMTP Capture
Captures every email sent to port 1025 as a raw .eml file with immutable JSON metadata. Zero config, zero risk.
Web UI
A clean, developer-focused web interface at port 8025 for browsing captured emails, viewing headers, body content, and metadata.
Email Replay
Re-send any captured email to a real SMTP server for testing forwarding rules, templates, and delivery pipelines.
REST API
Full HTTP API for listing, inspecting, exporting, and replaying emails. Integrates with any CI/CD pipeline or testing framework.
CLI Tool
A lightweight CLI (deadletterctl) for scripting against the HTTP API. List, show, replay, and export emails from the terminal.
Retention Policy
Configurable retention in minutes controls how long messages are kept. Cleanup can be triggered manually or runs automatically.
Web Interface
Getting Started
SMTP: localhost:1025HTTP: localhost:8025
docker run -d \
--name deadletter \
-p 1025:1025 \
-p 8025:8025 \
-v "$PWD/data:/data" \
peixotomdb/deadletter:latestAPI Reference
/health/emails/emails/{id}/emails/{id}/raw/config/replay/config/replay/replay/eventsCLI
# list all emails
go run ./cmd/deadletterctl list
# inspect metadata
go run ./cmd/deadletterctl show <id>
# replay / export
go run ./cmd/deadletterctl replay <id>
go run ./cmd/deadletterctl export <id> eml
go run ./cmd/deadletterctl export <id> json