MX Probe
Email verification for AI agents. One call returns send, hold or killfor an address, with the reason. Signup and credits happen by API too, so anoutreach agent can provision itself. No form, no CAPTCHA, no dashboard.
- Site and docs: https://mxprobe.dev
- API: https://api.mxprobe.dev (it describes itself on
GET /). OpenAPI: https://mxprobe.dev/openapi.json. For agents: https://mxprobe.dev/llms.txt - npm:
mxprobe(CLI + MCP server),mxprobe-core(the engine)
npx mxprobe check [email protected] # free DNS tier, local, no key
npx mxprobe check --hosted [email protected] # survivors go to the hosted SMTP probe
claude mcp add mxprobe -- npx -y mxprobe mcp # the MCP server
One click: Cursor · VS Code ·LM Studio. In Claude Code the same server also comes as a plugin:/plugin marketplace add andrewchmr/mxprobe, then /plugin install mxprobe@mxprobe.
{
"email": "[email protected]",
"action": "send",
"verdict": "OK",
"reason": "mailbox accepted by aspmx.l.google.com",
"checks": { "syntax": true, "mx": "aspmx.l.google.com", "smtp": "accepted", "catch_all": false }
}
action is send, hold or kill; verdict is OK, WEAK or DEAD. Ahold never becomes a kill on a refusal, a greylist or a catch-all. Only a5xx that names the mailbox kills.
Layout
| Path | What |
|---|---|
packages/core |
The engine: DNS tier, SMTP probe, the verdict contract and the API's wire types. Zero dependencies. |
packages/cli |
`npx mxprobe check |
server |
The hosted API: node:http + node:sqlite, Stripe Checkout, Resend, Telegram. |
site |
The landing page, static. |
deploy |
Caddyfile, systemd units, the install script and the runbook. |
Develop
Everything is TypeScript (strict, ESM). Each package compiles its src/ todist/ with tsc -b; the published packages ship dist/ only. mxprobe andthe server import mxprobe-core through the workspace link to its dist/,so pnpm build at the root (which runs the packages in dependency order) mustcome before a single package's test or typecheck. Tests are .ts filesthat Node runs directly with its built-in type stripping.
pnpm install
pnpm build # tsc -b in each package, core first
pnpm test # builds, then: fake resolver, fake SMTP server, in-memory SQLite. No network.
pnpm typecheck # the sources and the tests, without emitting
pnpm test:live # the DNS tier against the real network
pnpm check [email protected] # the CLI from this checkout
cp server/.env.example server/.env && pnpm dev:server
Node 22.18 or newer (24 recommended) to develop and to run the tests; thecompiled engine and CLI run on Node 20, the server on 22.13 or newer(node:sqlite).
Pricing
100 checks free at signup, then 9 USD per 10,000, one payment, credits neverexpire. Addresses are logged for 24 hours for debugging and then deleted.
MIT.
