maelsink

A single-binary fake SMTP server for local development and CI. It accepts any mail over SMTP and lets you inspect it — it never relays mail anywhere.

Install

Pick one of four ways to get maelsink, all built from the same tagged release so every install path ships with a working, embedded Web UI:

1. Download a binary from the GitHub Releases page — pick the archive matching your OS/arch, extract, run.
2. Homebrew (macOS/Linux):

   brew install 0funct0ry/maelsink/maelsink

3. Scoop (Windows):

   scoop bucket add maelsink https://github.com/0funct0ry/scoop-maelsink
   scoop install maelsink

4. Docker:

   docker run --rm -p 1025:1025 -p 8080:8080 -p 9090:9090 \
     -v maelsink-data:/data ghcr.io/0funct0ry/maelsink:latest

   Or via Compose: docker compose up (see docker-compose.yml).

go install is deliberately not offered — it skips the frontend build step, so a binary built that way would ship without a working Web UI.

Releases (binaries/Homebrew/Scoop) are cut via a manually triggered GitHub Actions workflow after a tag is pushed; the Docker image is published as a separate manual step.

Prerequisites

• Go 1.26+

Build & run

make build
make run

This starts maelsink with its default configuration:

Service	Default address
SMTP	127.0.0.1:1025
Web UI	http://127.0.0.1:8080/
REST API	http://127.0.0.1:9090/api/v1

Point your application's SMTP client at localhost:1025 and send mail — it'll show up in maelsink.

By default (no -d/--db given, and no storage.path set via config file or env var) maelsink stores messages in a transient in-memory SQLite database — nothing is written to disk, and all messages are lost when the process exits. The startup log states which storage mode is active. Pass --db <path> (e.g. --db ./maelsink.db) for a persistent, file-backed database; passing --db with no value at all (or --db "" explicitly) falls back to the default file, ./maelsink.db, in the current directory.

By default maelsink only listens on 127.0.0.1 (loopback) — it's a development tool and isn't meant to be exposed on a network. To bind elsewhere (e.g. 0.0.0.0 inside a container), set --smtp-host, --web-host, --api-host (or the matching MAELSINK_*_HOST env vars / config keys) explicitly, and enable smtp.auth/api.auth first if you do.

Configuration

Generate a default config file, then inspect the effective (fully resolved) config at any time:

./bin/maelsink config init    # writes ./maelsink.yaml
./bin/maelsink config show    # prints the resolved config as YAML

Configuration can also be set via MAELSINK_* environment variables or CLI flags — run ./bin/maelsink --help or ./bin/maelsink serve --help for the full flag list.

Other useful commands

make test   # run the test suite
make fmt    # format Go source
make vet    # run go vet

Documentation

• docs/cli-smtp-tls.md — using maelsink send/shell against a TLS/auth-hardened SMTP listener
• docs/deployment.md — deployment guide
• docs/reverse-proxy.md — running the Web UI behind a reverse proxy