Postwire 🌲📬

A tiny, single-binary SMTP & SMS catcher for development environments — like Mailtrap or Mailpit, but written in Rust with a minimal footprint (~15MB image), structured as a monorepo, and built for agentic development: AI agents (and e2e tests) can discover, wait for, and extract data from captured emails and SMS messages via a REST API or an MCP server.

Tags: mail • SMTP • SMS • mail-catcher • sms-catcher • testing • e2e • agents • MCP • Docker • Rust • email • development

Monorepo Layout

crates/core/    postwire-core   — shared SQLite store, MIME parsing, HTML/spam analysis, signal extraction
crates/server/  postwire        — SMTP (1025) + HTTP API/UI (8025); what you deploy
crates/mcp/     postwire-mcp    — MCP stdio server exposing emails & SMS to AI agents
apps/web/                       — React + Vite + TS frontend embedded into `postwire`

For full system architecture, sequence diagrams, database schemas, and design details, see ARCHITECTURE.md.
For runtime integration details for AI agents and test suites, see AGENTS.md.

Feature Comparison

Feature	Postwire 🌲	Mailhog	Mailpit	Mailtrap (SaaS)
Single Static Binary	✅ (Rust, ~15MB)	❌ (Go + deps)	✅ (Go)	❌ (Cloud SaaS only)
Dual Email & SMS Catcher	✅ Built-in	❌ Email only	❌ Email only	🟡 Partial
Twilio Webhook Ingestion	✅ Built-in	❌	❌	❌
Auto Signal Extraction (OTP / Links)	✅ Built-in	❌	❌	❌
Long-Polling Wait API (`/api/wait` & `/api/sms/wait`)	✅ Built-in	❌	🟡 Partial	❌
Litmus-Style Email Analysis	✅ Built-in	❌	❌	❌
14 MCP Tools for AI Agents	✅ Built-in	❌	❌	❌
Free & Open Source	✅ MIT	✅	✅	❌

Key Features

SMTP Email Catcher (:1025): dead-end local SMTP listener (no auth, no relaying, no external network calls).
SMS Catcher & Twilio Webhook Support (:8025): ingest SMS via standard JSON (POST /api/sms) or Twilio webhooks (POST /api/sms/webhook with x-www-form-urlencoded payloads).
Dual-Tab Web UI & REST API (:8025): clean React interface for viewing both Emails and SMS messages with live WebSocket updates.
Rich Message Inspection: view HTML/plain-text bodies, raw headers, download attachments or raw .eml files.
Litmus-Style Email Analysis: GET /api/messages/:id/analysis checks 11 HTML email-client compatibility factors (DOCTYPE, tables, inline CSS, fonts, image alt, size clipping) and provides a SpamAssassin-style heuristic spam score.
Search, Pagination & Bulk Actions: multi-select grid with bulk mark read/unread, bulk delete, and paginated lazy-loading (50 items per page).
Agentic Long-Polling: GET /api/wait and GET /api/sms/wait long-poll server-side for incoming emails or SMS matching filters (to, from, subject, body, since).
Signal Extraction Engine: GET /api/messages/:id/extract and GET /api/sms/:id/extract automatically pull OTP codes (4–8 digits) and magic links out of captured emails and SMS bodies.
14 MCP Agent Tools (postwire-mcp): Model Context Protocol stdio server exposing 7 Email tools and 7 SMS tools directly to Claude Desktop, Copilot, Cursor, and autonomous test runners.
SQLite Storage: persistent SQLite storage (/data/postwire.db or :memory:) with automatic FIFO pruning past MAX_MESSAGES.
Zero External Runtime Dependencies: single binary with embedded frontend built via rust-embed.

Installation & Distribution Methods

Postwire provides official distribution packages and single static binaries for macOS, Linux, and Windows.

🍺 Homebrew (macOS & Linux)

Install Postwire from the canonical project and release assets in yoosuf/postwire. The existing Homebrew formula remains available under its legacy postwire package/service name, while the project itself is now branded as Postwire and the release archives provide the new postwire commands.

# Add the Homebrew tap and install
brew tap yoosuf/tap
brew install postwire

# Or install directly in a single command:
brew install yoosuf/tap/postwire

Manage as a background service (macOS & Linux):

# Start Postwire as a background service (SMTP on :1025, Web UI & API on :8025)
brew services start postwire

# Check service status, stop, or restart
brew services info postwire
brew services stop postwire
brew services restart postwire

⚡ Automated One-Liner Installers

Auto-detects OS and CPU architecture, downloads the latest binary release, and places executables in PATH.

macOS & Linux (POSIX Shell):

curl -fsSL https://raw.githubusercontent.com/yoosuf/postwire/main/install.sh | sh

Windows (PowerShell):

iwr -useb https://raw.githubusercontent.com/yoosuf/postwire/main/install.ps1 | iex

🐧 Linux Native Packages

Debian / Ubuntu (.deb):

curl -LO https://github.com/yoosuf/postwire/releases/latest/download/postwire_amd64.deb
sudo dpkg -i postwire_amd64.deb

Fedora / RHEL / CentOS (.rpm):

sudo rpm -i https://github.com/yoosuf/postwire/releases/latest/download/postwire.x86_64.rpm

Arch Linux (AUR):
```
yay -S postwire-bin
```

🪟 Windows Package Managers

Scoop:

scoop bucket add postwire https://github.com/yoosuf/scoop-bucket
scoop install postwire

Winget (Windows Package Manager):
```
winget install Postwire.Postwire
```
Chocolatey:
```
choco install postwire
```

📦 Pre-Compiled GitHub Release Binaries

Download standalone pre-built binaries from GitHub Releases:

Operating System	Architecture	Package File
macOS	Apple Silicon (`aarch64`)	`postwire-v*-aarch64-apple-darwin.tar.gz`
macOS	Intel (`x86_64`)	`postwire-v*-x86_64-apple-darwin.tar.gz`
Linux	x86_64	`postwire-v*-x86_64-unknown-linux-gnu.tar.gz`
Linux	ARM64 (`aarch64`)	`postwire-v*-aarch64-unknown-linux-gnu.tar.gz`
Windows	x86_64	`postwire-v*-x86_64-pc-windows-msvc.zip`

Each archive also includes the legacy postwire and postwire-mcp command names.

🦀 Cargo (Rust Workspace)

Install directly via cargo:

cargo install --git https://github.com/yoosuf/postwire postwire-server --bin postwire
cargo install --git https://github.com/yoosuf/postwire postwire-mcp --bin postwire-mcp

🐳 Docker & Docker Compose

Pull the published multi-arch image (linux/amd64 + linux/arm64) from Docker Hub:

docker run -d --name postwire -p 1025:1025 -p 8025:8025 -v postwire-data:/data yoosuf/postwire:latest

Or run via Docker Compose:

docker compose up --build

To run the MCP server against it:

docker compose --profile mcp run --rm mcp

Docker Hub: yoosuf/postwire — canonical Postwire image; legacy yoosuf/postwire tags remain available for compatibility.

Agent Integration Examples

REST API (Long-Polling + Signal Extraction)

# 1. Long-poll for a fresh email matching criteria (up to 10s default, max 60s)
curl "http://localhost:8025/api/[email protected]&subject=Verify&since=2026-09-04T09:00:00Z"

# 2. Extract OTP codes and links from the received email
curl "http://localhost:8025/api/messages/<MESSAGE_ID>/extract"
# Response: { "codes": ["482913"], "links": ["https://app.test/verify?token=..."] }

# 3. Analyze HTML compatibility & spam score
curl "http://localhost:8025/api/messages/<MESSAGE_ID>/analysis"

# 4. Long-poll for a fresh SMS message
curl "http://localhost:8025/api/sms/wait?to=+15550100&since=2026-09-04T09:00:00Z"

# 5. Extract OTP codes from the received SMS
curl "http://localhost:8025/api/sms/<SMS_ID>/extract"
# Response: { "codes": ["940182"], "links": [] }

Twilio SMS Ingestion Webhook

Point your application or local webhook relay to:

POST http://localhost:8025/api/sms/webhook
Content-Type: application/x-www-form-urlencoded

From=%2B15550199&To=%2B15550100&Body=Your+verification+code+is+839201

Node.js (E2E Test Automation)

Using Node 18+ native fetch to wait for messages and extract OTP verification codes:

// 1. Capture ISO timestamp BEFORE triggering signup / SMS 2FA action
const since = new Date().toISOString();
const userPhone = "+15550199";

// 2. Trigger your application action (e.g. request 2FA SMS code)
await triggerSmsCodeAction({ to: userPhone });

// 3. Long-poll Postwire server-side until SMS arrives (blocks up to timeout_ms)
const waitRes = await fetch(
  `http://localhost:8025/api/sms/wait?to=${encodeURIComponent(userPhone)}&since=${since}&timeout_ms=10000`
);
const sms = await waitRes.json();

// 4. Extract 4-8 digit OTP verification code
const extractRes = await fetch(`http://localhost:8025/api/sms/${sms.id}/extract`);
const { codes } = await extractRes.json();
const otpCode = codes[0]; // e.g. "839201"

// 5. Submit extracted OTP code into your test runner / app
await submitOtpCode(otpCode);

REST API Directory

Email Endpoints (`/api/messages`)

Method	Endpoint	Description
`GET`	`/api/messages`	List captured emails (`search`, `limit`, `offset`)
`GET`	`/api/messages/:id`	Fetch full email details (headers, text/html, attachments)
`GET`	`/api/messages/:id/raw`	Download raw MIME file (`.eml`)
`GET`	`/api/messages/:id/html`	Render raw HTML body
`GET`	`/api/messages/:id/attachments/:index`	Download attachment by index
`GET`	`/api/messages/:id/extract`	Extract OTP codes (4-8 digits) and HTTP/HTTPS links
`GET`	`/api/messages/:id/analysis`	HTML email compatibility checks & heuristic spam score
`GET`	`/api/wait`	Server-side long-polling wait (`to`, `from`, `subject`, `since`, `timeout_ms`)
`PATCH`	`/api/messages/:id/read`	Toggle read/unread state
`DELETE`	`/api/messages/:id`	Delete email by ID
`POST`	`/api/messages/bulk-delete`	Bulk delete emails by ID list
`PATCH`	`/api/messages/bulk-read`	Bulk update read state
`DELETE`	`/api/messages`	Clear all emails
`POST`	`/api/test-email`	Inject synthetic test email

SMS Endpoints (`/api/sms`)

Method	Endpoint	Description
`GET`	`/api/sms`	List captured SMS messages (`search`, `limit`, `offset`)
`GET`	`/api/sms/:id`	Fetch single SMS details
`POST`	`/api/sms`	Ingest SMS via JSON payload
`POST`	`/api/sms/webhook`	Ingest SMS via Twilio form-urlencoded or JSON webhook
`GET`	`/api/sms/wait`	Server-side long-polling wait for SMS (`to`, `from`, `body`, `since`, `timeout_ms`)
`GET`	`/api/sms/:id/extract`	Extract OTP codes (4-8 digits) and HTTP/HTTPS links from SMS
`PATCH`	`/api/sms/:id/read`	Toggle read/unread state
`DELETE`	`/api/sms/:id`	Delete SMS by ID
`POST`	`/api/sms/bulk-delete`	Bulk delete SMS by ID list
`PATCH`	`/api/sms/bulk-read`	Bulk update SMS read state
`DELETE`	`/api/sms`	Clear all SMS messages
`POST`	`/api/test-sms`	Inject synthetic test SMS message

Model Context Protocol (MCP) Server (`postwire-mcp`)

Postwire includes 14 built-in MCP tools for AI agents (Claude Desktop, Copilot, Cursor, agentic E2E tests):

Category	Tool Name	Parameters	Description
Email Tools	`list_emails`	`search?`, `limit?`, `offset?`	Query emails with search filter and pagination
	`get_email`	`id`	Get email headers, text/html content, and attachment metadata
	`wait_for_email`	`to?`, `from?`, `subject?`, `since_ms?`, `timeout_ms?`	Long-poll server-side until matching email arrives
	`extract_signals`	`id`	Automatically extract OTP codes and links from email
	`send_test_email`	`to?`	Inject synthetic test email
	`delete_email`	`id`	Delete email by ID
	`clear_inbox`	none	Clear all emails
SMS Tools	`list_sms`	`search?`, `limit?`, `offset?`	Query captured SMS with search filter and pagination
	`get_sms`	`id`	Get single SMS details
	`wait_for_sms`	`to?`, `from?`, `body?`, `since_ms?`, `timeout_ms?`	Long-poll server-side until matching SMS arrives
	`extract_sms_signals`	`id`	Automatically extract OTP codes and links from SMS body
	`send_test_sms`	`to?`, `from?`, `body?`	Inject synthetic test SMS
	`delete_sms`	`id`	Delete SMS by ID
	`clear_sms_inbox`	none	Clear all SMS messages

Configuration (Environment Variables)

Variable	Default	Description
`POSTWIRE_SMTP_PORT`	`1025`	SMTP listener port; `SMTP_PORT` remains a legacy alias
`POSTWIRE_HTTP_PORT`	`8025`	Web UI / REST API port; `HTTP_PORT` remains a legacy alias
`POSTWIRE_BIND_ADDR`	`0.0.0.0`	Bind address; `BIND_ADDR` remains a legacy alias
`POSTWIRE_DB_PATH`	`postwire.db` (`/data/postwire.db` in Docker)	SQLite path; `DB_PATH` remains a legacy alias and the default preserves existing data
`POSTWIRE_MAX_MESSAGES`	`1000`	FIFO limit (`0` = unlimited); `MAX_MESSAGES` remains a legacy alias
`POSTWIRE_TTL_SECONDS`	`0`	Remove messages/SMS older than this many seconds on ingestion; `TTL_SECONDS` remains a legacy alias
`POSTWIRE_SMTP_HOSTNAME`	`postwire`	SMTP banner hostname; `SMTP_HOSTNAME` remains a legacy alias
`POSTWIRE_URL`	`http://127.0.0.1:8025`	(`postwire-mcp` only) Server URL; `POSTWIRE_URL` remains a legacy alias

Local Development

# Terminal 1 — Frontend hot reload (Vite dev server proxied to Rust API)
cd apps/web && npm install && npm run dev

# Terminal 2 — Backend server (SMTP on :1025, API on :8025)
cargo run -p postwire-server --bin postwire

Building Release Binaries

cd apps/web && npm install && npm run build && cd ..
cargo build --release --workspace

The frontend static assets must be built to apps/web/dist before building postwire-server, as they are embedded directly into the postwire binary using rust-embed.

Author

Built by Yoosuf, who also offers fractional CTO services.

Name		Name	Last commit message	Last commit date
.github/workflows		.github/workflows
apps/web		apps/web
crates		crates
docs		docs
examples		examples
.dockerignore		.dockerignore
.gitignore		.gitignore
AGENTS.md		AGENTS.md
ARCHITECTURE.md		ARCHITECTURE.md
Cargo.lock		Cargo.lock
Cargo.toml		Cargo.toml
DOCKERHUB.md		DOCKERHUB.md
Dockerfile		Dockerfile
README.md		README.md
docker-compose.yml		docker-compose.yml
install.ps1		install.ps1
install.sh		install.sh

Navigation Menu

Repository files navigation

Postwire 🌲📬

Monorepo Layout

Feature Comparison

Key Features

Installation & Distribution Methods

🍺 Homebrew (macOS & Linux)

⚡ Automated One-Liner Installers

🐧 Linux Native Packages

🪟 Windows Package Managers

📦 Pre-Compiled GitHub Release Binaries

🦀 Cargo (Rust Workspace)

🐳 Docker & Docker Compose

Agent Integration Examples

REST API (Long-Polling + Signal Extraction)

Twilio SMS Ingestion Webhook

Node.js (E2E Test Automation)

REST API Directory

Email Endpoints (`/api/messages`)

SMS Endpoints (`/api/sms`)

Model Context Protocol (MCP) Server (`postwire-mcp`)

Configuration (Environment Variables)

Local Development

Building Release Binaries

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Postwire 🌲📬

Monorepo Layout

Feature Comparison

Key Features

Installation & Distribution Methods

🍺 Homebrew (macOS & Linux)

⚡ Automated One-Liner Installers

🐧 Linux Native Packages

🪟 Windows Package Managers

📦 Pre-Compiled GitHub Release Binaries

🦀 Cargo (Rust Workspace)

🐳 Docker & Docker Compose

Agent Integration Examples

REST API (Long-Polling + Signal Extraction)

Twilio SMS Ingestion Webhook

Node.js (E2E Test Automation)

REST API Directory

Email Endpoints (/api/messages)

SMS Endpoints (/api/sms)

Model Context Protocol (MCP) Server (postwire-mcp)

Configuration (Environment Variables)

Local Development

Building Release Binaries

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Email Endpoints (`/api/messages`)

SMS Endpoints (`/api/sms`)

Model Context Protocol (MCP) Server (`postwire-mcp`)