Email Validator MCP

An MCP server for checking email syntax and DNS mail routes without sending a message. Optional SMTP probing provides a recipient acceptance signal; it does not prove ownership or guarantee delivery.

Install a published release

Requires uv:

uvx --python 3.13 mcp-email-validator@0.2.0

Published versions are listed on PyPI. If the version is not available yet, use the GitHub command below. Publishing is managed through GitHub Actions.

Run from GitHub without cloning

Requires uv and Git. uv downloads the selected package and manages Python 3.13 and its dependencies:

uvx --python 3.13 --from "git+https://github.com/jayanth-mkv/agent-mcp-registry.git@main#subdirectory=mcp-email-validator" mcp-email-validator

Only this MCP and its runtime dependencies are installed. uv fetches the repository internally; you do not need a local checkout. To pin the source, replace main with a release tag or full commit SHA.

Install from source

From this directory, with Python 3.13+ and uv:

uv sync --locked --no-dev
uv run --locked --no-dev mcp-email-validator

The default transport is stdio. Configure your MCP client using the repository example. No API key is required; DNS checks need network access.

For Streamable HTTP:

uv run --locked --no-dev mcp-email-validator --transport http --host 127.0.0.1 --port 8003

Endpoint: http://127.0.0.1:8003/mcp. Legacy SSE is available with --transport sse at /sse. HTTP and SSE have no authentication; keep them on loopback unless protected separately.

Tools

Both tools check conventional unquoted mailbox syntax and normalize the domain, then look up MX records. Domains without MX records may use A/AAAA fallback; a null MX means the domain does not accept mail. Invalid syntax skips DNS and SMTP.

Example tool arguments:

{ "address": "user@example.com", "check_smtp": false }

Results contain normalized_address, syntax_valid, mail_route_status, mail_hosts, smtp_status, and explanatory notes.

SMTP boundaries

SMTP probing is disabled unless check_smtp=true. It tries at most three mail hosts, connects to one public IP per host on port 25, and uses SMTP greeting, sender, and recipient commands. It never sends DATA or authenticates. DNS lookups and socket operations use a timeout clamped to 1–15 seconds; this is not a total request deadline, and batches run sequentially.

Use probing only for infrastructure and addresses you are authorized to assess. Catch-all domains, greylisting, sender policy, and anti-abuse controls can produce misleading results. Private and loopback IP addresses are not contacted. Address data is not written to an application database; DNS queries and optional SMTP probes are visible to the contacted infrastructure.

Development

uv sync --locked
uv run --locked pytest -q
uv build

Tests mock DNS/SMTP network operations and exercise the installed stdio server. Live recipient acceptance and delivery are separate checks.

Version 0.2.0. Licensed under the MIT License.