MailTester Ninja MCP

The official remote MCP server for MailTester Ninja allows AI agents to verify email addresses live against recipient mail servers and find work emails from names and company domains. It provides tools for checking deliverability and discovering contacts without storing any data.

Endpoint and access

No sign-in to connect and list tools. Individual tools may still need a vendor account, credentials, or permissions; check the documented prerequisites.

Vendor evidenceStreamable HTTPNo sign-inEndpoint checked 2026-11-01Operated by MailTester Ninja

You need:A key: a free API token to try verify_email (50 checks a day, one request every 30 seconds), or a paid key for full speed and for find_emailAn MCP client that supports remote servers over Streamable HTTP

MCP endpoint (Streamable HTTP)

https://mcp.mailtester.ninja/mcp

Vendor documentation

What you can do with it

Check whether an email address exists and can receive mail
Find the work email of a person at a company
Check signups to tell which ones will bounce

Source and maintenance

Vendor evidenceRegistry 1.0.1

mcp-registry: ninja.mailtester/email-verification@1.0.1 Project website

Protocol and capabilities

Server: mailtester-ninja 1.2.1
MCP protocol: 2025-06-18
Tools: 2 advertised
Resources: Not advertised
Resource templates: Not advertised
Prompts: Not advertised

Server-advertised capabilities

{
  "tools": {
    "listChanged": true
  }
}

Server-provided instructions

Untrusted server output shown for inspection. It is not Koskamo guidance and is excluded from knowledge search.

MailTester Ninja checks email addresses in real time against the recipient's mail server, without sending any message. verify_email returns a code: "ok" (valid and deliverable), "ko" (invalid, will bounce) or "mb" (uncertain, for example a catch-all domain that accepts every address), plus a message such as Accepted, Rejected, Catch-All, No MX or Disposable. Report the verdict the tool returned, never guess one, and treat "mb" as uncertain rather than valid. find_email tries the usual address patterns for a person at a company domain and returns the first one the mail server accepts. Every check, including each pattern tried by find_email, counts against the user's daily quota.

Tools

2 advertised

verify_email — Verify an email address

Advertised by the server during the last successful anonymous check.

Advertised read-onlyOpen-world

Check in real time whether an email address exists and can receive mail, by asking the recipient's mail server (no message is sent). Returns code "ok" (valid), "ko" (invalid) or "mb" (uncertain, such as a catch-all domain) with a message.

verify_email input schema

{
  "type": "object",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "required": [
    "email"
  ],
  "properties": {
    "email": {
      "type": "string",
      "maxLength": 254,
      "minLength": 3,
      "description": "The email address to verify"
    }
  }
}

verify_email output schema

{
  "type": "object",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "required": [
    "email",
    "code",
    "message",
    "domain",
    "mx"
  ],
  "properties": {
    "mx": {
      "type": "string"
    },
    "code": {
      "type": "string",
      "description": "\"ok\" valid, \"ko\" invalid, \"mb\" uncertain"
    },
    "email": {
      "type": "string"
    },
    "domain": {
      "type": [
        "string",
        "null"
      ]
    },
    "message": {
      "type": "string",
      "description": "Accepted, Rejected, Catch-All, No MX, Disposable, Timeout..."
    }
  },
  "additionalProperties": false
}

verify_email annotations

{
  "title": "Verify an email address",
  "readOnlyHint": true,
  "openWorldHint": true,
  "idempotentHint": true,
  "destructiveHint": false
}

find_email — Find a professional email address

Advertised by the server during the last successful anonymous check.

Advertised read-onlyOpen-world

Find the work email address of a person from their name and their company domain. Tries the 6 most common patterns (first.last, flast, first, firstlast, first_last, f.last) one by one and returns the first address the mail server accepts. Stops early when the domain accepts every address (catch-all) and then gives the most common pattern as "guess". Each pattern tried counts as one verification. Personal email providers such as gmail.com are not searched. Requires a paid MailTester Ninja key.

find_email input schema

{
  "type": "object",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "required": [
    "first_name",
    "last_name",
    "domain"
  ],
  "properties": {
    "domain": {
      "type": "string",
      "maxLength": 253,
      "minLength": 3,
      "description": "Company domain, for example example.com"
    },
    "last_name": {
      "type": "string",
      "maxLength": 64,
      "minLength": 1,
      "description": "Last name, for example De La Tour"
    },
    "first_name": {
      "type": "string",
      "maxLength": 64,
      "minLength": 1,
      "description": "First name, for example Jean-Pierre"
    }
  }
}

find_email output schema

{
  "type": "object",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "required": [
    "found",
    "email",
    "format",
    "confidence",
    "guess",
    "code",
    "message",
    "tried",
    "tested",
    "reason"
  ],
  "properties": {
    "code": {
      "type": "string"
    },
    "email": {
      "type": [
        "string",
        "null"
      ],
      "description": "The address the mail server accepted, when found"
    },
    "found": {
      "type": "boolean"
    },
    "guess": {
      "type": [
        "string",
        "null"
      ],
      "description": "On a catch-all domain, the most common pattern; for a full mailbox, that address. Not verified."
    },
    "tried": {
      "type": "integer",
      "maximum": 9007199254740991,
      "minimum": -9007199254740991,
      "description": "Number of address patterns checked, each one counted as a verification"
    },
    "format": {
      "type": [
        "string",
        "null"
      ],
      "description": "Pattern of the returned address: first.last, flast, first, firstlast, first_last or f.last"
    },
    "reason": {
      "type": [
        "string",
        "null"
      ]
    },
    "tested": {
      "type": "array",
      "items": {
        "type": "object",
        "required": [
          "email",
          "code",
          "message"
        ],
        "properties": {
          "code": {
            "type": "string"
          },
          "email": {
            "type": "string"
          },
          "message": {
            "type": "string"
          }
        },
        "additionalProperties": false
      },
      "description": "Every address checked, in order, with its verdict"
    },
    "message": {
      "type": "string"
    },
    "confidence": {
      "anyOf": [
        {
          "enum": [
            "high",
            "medium",
            "low"
          ],
          "type": "string"
        },
        {
          "type": "null"
        }
      ],
      "description": "For an address found: high (first and last name in it), medium (an initial, a namesake may share it), low (first name only)"
    }
  },
  "additionalProperties": false
}

find_email annotations

{
  "title": "Find a professional email address",
  "readOnlyHint": true,
  "openWorldHint": true,
  "idempotentHint": true,
  "destructiveHint": false
}

Prompts

Not advertised

No prompt definitions available.

Resources

Not advertised

No resource definitions available.

30-day availability

Aggregated from read-only remote checks; this is not a tool-execution or security guarantee.

Successful checks: 1 of 1 (100%)
Average latency: 1059 ms
95th percentile latency: 1059 ms

Maintenance history

Public check and source-refresh events. Editorial and ownership records remain private.

Nov 1, 2026, 8:14 AM UTC · probe · passed · 1059 ms · metadata changed · 2 tool(s)

Connect from your client

Each snippet registers the same endpoint; pick the client you use.

This server is operated by the named third party. Listing and endpoint checks are not an endorsement or a security audit. Review the operator's permissions, terms, and data handling before connecting. How listings are checked and corrected.

Claude Code

Run this once in a terminal. It registers the remote server. Use --scope project to write .mcp.json for the repo.

Claude Code configuration

claude mcp add --transport http mailtester-ninja-mcp https://mcp.mailtester.ninja/mcp

Codex

Run this once. Codex stores MCP servers in ~/.codex/config.toml (or .codex/config.toml in a trusted project).

Codex configuration

codex mcp add mailtester-ninja-mcp --url https://mcp.mailtester.ninja/mcp

Cursor

Merge this server into .cursor/mcp.json in your project, then enable mailtester-ninja-mcp in your MCP settings.

Cursor configuration

{
  "mcpServers": {
    "mailtester-ninja-mcp": {
      "url": "https://mcp.mailtester.ninja/mcp"
    }
  }
}

Cline

Merge this into cline_mcp_settings.json (Cline → MCP Servers → Configure).

Cline configuration

{
  "mcpServers": {
    "mailtester-ninja-mcp": {
      "type": "streamableHttp",
      "url": "https://mcp.mailtester.ninja/mcp",
      "disabled": false
    }
  }
}

VS Code

Merge this server into .vscode/mcp.json. Use MCP: List Servers to start mailtester-ninja-mcp and inspect its tools.

VS Code configuration

{
  "servers": {
    "mailtester-ninja-mcp": {
      "type": "http",
      "url": "https://mcp.mailtester.ninja/mcp"
    }
  }
}

Gemini CLI

Run this once. It writes .gemini/settings.json in the current project; pass --scope user for ~/.gemini/settings.json.

Gemini CLI configuration

gemini mcp add --transport http mailtester-ninja-mcp https://mcp.mailtester.ninja/mcp

Claude Desktop

Merge this into claude_desktop_config.json (macOS: ~/Library/Application Support/Claude/, Windows: %APPDATA%\Claude\), then restart Claude Desktop.

Claude Desktop configuration

{
  "mcpServers": {
    "mailtester-ninja-mcp": {
      "url": "https://mcp.mailtester.ninja/mcp"
    }
  }
}

Windsurf

Merge this into ~/.codeium/windsurf/mcp_config.json, then refresh MCP in Cascade. Windsurf remote servers use serverUrl, not url.

Windsurf configuration

{
  "mcpServers": {
    "mailtester-ninja-mcp": {
      "serverUrl": "https://mcp.mailtester.ninja/mcp"
    }
  }
}

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