smtp-probe

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Open-source SMTP deliverability diagnostic tool — SPF/DKIM/DMARC checks, SMTP verification & RBL blacklist scanning

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# smtp-probe

[![Go Version](https://img.shields.io/github/go-mod/go-version/monto-fe/smtp-probe)](https://raw.githubusercontent.com/monto-fe/smtp-probe/main/go.mod)
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[中文文档](README_CN.md)

**Powered by [uSpeedo](https://uspeedo.com/?channal_code=GITHUB)** — production-ready global email delivery API.

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---

An open-source email deliverability diagnostic tool. Check SPF/DKIM/DMARC configuration, verify email addresses via SMTP, and scan IPs against 29 RBL blacklists — all from a single CLI or HTTP API.

## Features

- **Domain Health Check** — SPF, DKIM, DMARC, MX, PTR records with 0–100 scoring
- **SMTP Email Verification** — RCPT TO check via MX servers with bind-IP support
- **IP Pool Management** — Multiple bind IPs with health checks and automatic failover
- **Multi-Node Coordination** — GeoIP-based routing across distributed nodes
- **Disposable Email Detection** — Detect temporary email providers with 4 upstream data sources (~8k–74k domains each)
- **Free Email Detection** — Detect free email providers (Gmail, Outlook, Yahoo, etc.) with auto-downloaded blocklist
- **RBL Blacklist Scan** — Check IPs against 29 blacklists (Spamhaus, Barracuda, SpamCop, etc.)
- **Latency Probing** — Measure connection latency from each pool IP to target domains
- **HTTP API** — RESTful JSON API for programmatic integration
- **Multiple Output Formats** — text (CLI table), JSON, Markdown

## Installation

### Quick Install (Recommended)

```bash
bash <(curl -fsSL https://raw.githubusercontent.com/monto-fe/smtp-probe/main/install.sh)
```

Or specify a version:

```bash
VERSION=v0.1.0 bash <(curl -fsSL https://raw.githubusercontent.com/monto-fe/smtp-probe/main/install.sh)
```

### From Source

```bash
go install github.com/monto-fe/smtp-probe@latest
```

## Usage

### Check Domain Configuration

```bash
smtp-probe check gmail.com
smtp-probe check example.com
```

### Verify Email Address (requires outbound port 25)

```bash
smtp-probe verify user@example.com
smtp-probe verify user@example.com --bind-ip 1.2.3.4 --timeout 30s
```

> [!NOTE]
> SMTP verification requires outbound access to port 25, which is commonly blocked by ISPs and cloud providers. The `check` command (DNS-based) works without port 25 and covers SPF/DKIM/DMARC/MX/PTR diagnostics.

### Verify with Disposable Email Detection

```bash
smtp-probe verify user@mailinator.com --disposable
```

On first use with `--disposable`, the default blocklist (martenson, ~8k domains, CC0) is downloaded automatically. If the email domain is disposable, SMTP verification is skipped.

### Verify with Free Email Detection

```bash
smtp-probe verify user@gmail.com --free
```

On first use with `--free`, the default free email list (dpup/freemail, ~4.5k domains, ISC) is downloaded automatically. Unlike disposable detection, SMTP verification **proceeds** after free email detection — it only annotates the result.

### Verify with IP Pool and Automatic Failover

```bash
# Add IPs to pool
smtp-probe pool add 1.2.3.4 --domain mail-a.example.com
smtp-probe pool add 1.2.3.5 --domain mail-b.example.com

# Verify with pool (auto-failover on blacklist/timeout)
smtp-probe verify user@example.com --pool

# Check pool health
smtp-probe pool list
smtp-probe pool check
```

When `--pool` is used, smtp-probe selects a healthy IP from the pool. If an IP gets blacklisted (5xx response), it's automatically marked and the next healthy IP is tried (up to 3 retries).

### Measure SMTP Latency

```bash
# Single probe from default outbound IP
smtp-probe probe gmail.com

# Probe from each IP in the pool
smtp-probe probe gmail.com --pool
```

### Multi-Node Deployment

Deploy multiple smtp-probe servers across different regions and coordinate them:

```bash
# Start node A in Singapore
smtp-probe serve --port 8080 \
  --node-id sg-01 --region asia-southeast1 \
  --lat 1.35 --lon 103.82 \
  --peers http://us-node:8080,http://eu-node:8080

# Start node B in US West
smtp-probe serve --port 8080 \
  --node-id us-01 --region us-west1 \
  --lat 37.77 --lon -122.42 \
  --peers http://sg-node:8080,http://eu-node:8080
```

Each node automatically:
- Registers with all peers via heartbeat (every 30s)
- Routes verification requests to the geographically closest node (based on MX server location)
- Falls back to local execution if remote node is unavailable

### Check IP Against Blacklists

```bash
smtp-probe blacklist 1.2.3.4
```

### Generate Full Report

```bash
smtp-probe report example.com
smtp-probe report example.com --format json
smtp-probe report example.com --format md > report.md
```

### Start HTTP Server

```bash
smtp-probe serve
smtp-probe serve --port 9090
# Multi-node with peers:
smtp-probe serve --port 8080 --node-id node-01 --peers http://10.0.0.2:8080
```

## HTTP API

| Endpoint | Method | Parameters |
|---|---|---|
| `/v1/health` | GET | — |
| `/v1/check` | GET | `domain=example.com` |
| `/v1/verify` | GET | `email=user@example.com`, `bind_ip=1.2.3.4`, `timeout=60s`, `disposable=true`, `free=true`, `pool=true` |
| `/v1/blacklist` | GET | `ip=1.2.3.4` |
| `/v1/report` | GET | `domain=example.com` |
| `/v1/peer/register` | POST | `{node_id, addr, region, lat, lon, pool_size}` (multi-node) |
| `/v1/peer/peers` | GET | — (list registered peers) |
| `/v1/peer/heartbeat` | POST | `{node_id, ...}` (multi-node heartbeat) |
| `/v1/peer/geo` | GET | `ip=1.2.3.4` (GeoIP lookup) |

```bash
curl http://localhost:8080/v1/check?domain=gmail.com
curl "http://localhost:8080/v1/verify?email=user@example.com"
curl http://localhost:8080/v1/blacklist?ip=1.2.3.4
```

## Scoring System

| Check | Deduction |
|---|---|
| No SPF | -20 |
| Invalid SPF | -10 |
| No DKIM | -15 |
| No DMARC | -20 |
| Weak DMARC (p=none) | -10 |
| No MX | -30 |

## Architecture

```
smtp-probe/
├── main.go                  # Entry point
├── cmd/                     # Cobra CLI commands
├── pkg/                     # Core packages
│   ├── probe/               # Orchestrator and scoring
│   ├── dnscheck/            # DNS record checks (SPF/DKIM/DMARC/MX/PTR)
│   ├── disposable/          # Disposable email domain detection
│   ├── freemail/            # Free email provider domain detection
│   ├── pool/                # IP pool management and health checks
│   ├── node/                # Multi-node coordination (GeoIP, routing, heartbeat)
│   ├── rbl/                 # RBL blacklist queries
│   ├── smtpclient/          # SMTP RCPT TO verification
│   └── types/               # Shared type definitions
└── server/                  # HTTP API (Gin)
```

## Configuration

### Verification Flags

| Flag | Default | Description |
|---|---|---|
| `--bind-ip` | (outbound IP) | Source IP for SMTP connections |
| `--timeout` | 60s | SMTP/DNS timeout |
| `--port` | 8080 | HTTP server port |
| `--format` | text | Output format: `json`, `md`, `text` |
| `--disposable` | false | Enable disposable email provider check |
| `--free` | false | Enable free email provider check |
| `--pool` | false | Use IP pool with automatic failover |

### IP Pool Management

```bash
# Add IP to pool
smtp-probe pool add 1.2.3.4 --domain mail-a.example.com

# Remove IP from pool
smtp-probe pool remove 1.2.3.4

# List all IPs and their status
smtp-probe pool list

# Check health of all IPs (RBL scan)
smtp-probe pool check

# Check health of a specific IP
smtp-probe pool check 1.2.3.4
```

Pool is persisted at `~/.smtp-probe/pool.json`.

### Multi-Node Flags

| Flag | Default | Description |
|---|---|---|
| `--node-id` | (auto) | Unique identifier for this node |
| `--region` | — | Region name (e.g., `asia-southeast1`, `us-west1`) |
| `--lat` | 0 | Node latitude |
| `--lon` | 0 | Node longitude |
| `--peers` | — | Initial peer addresses (comma-separated) |
| `--heartbeat` | 30s | Heartbeat interval for peer nodes |

### Managing Disposable Email Lists

```bash
# List all sources and their status
smtp-probe disposable list

# Download specific sources
smtp-probe disposable download disposable fakefilter

# Download all available sources
smtp-probe disposable download --all

# Update stale lists (re-downloads if older than 7 days)
smtp-probe disposable update

# Install daily auto-update via crontab
smtp-probe disposable update --install-cron
```

| Source | Domains | Default | Description |
|---|---|---|---|
| `martenson` | ~8k | Yes | CC0 blocklist used by PyPI |
| `disposable` | ~74k | No | Multi-source aggregation |
| `tompec` | ~20k | No | Successor to ivolo (suffix mode) |
| `fakefilter` | ~10k | No | Automated monitoring |

### Managing Free Email Lists

```bash
# List all sources and their status
smtp-probe freemail list

# Download the default source
smtp-probe freemail download

# Download all available sources
smtp-probe freemail download --all

# Update stale lists (re-downloads if older than 7 days)
smtp-probe freemail update

# Install daily auto-update via crontab
smtp-probe freemail update --install-cron
```

| Source | Domains | Default | Description |
|---|---|---|---|
| `dpup` | ~4.5k | Yes | dpup/freemail community list |

## Development

```bash
git clone https://github.com/monto-fe/smtp-probe.git
cd smtp-probe
go build -o smtp-probe .
go test ./...
```

## Contributing

1. Fork the repository
2. Create your feature branch (`git checkout -b feature/amazing`)
3. Run tests: `go test ./...`
4. Run linter: `golangci-lint run`
5. Commit your changes
6. Open a Pull Request

## License

MIT — see [LICENSE](LICENSE)

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