MailTester Email Verification

Official9 tools

by mailtester-com

Verify emails (valid/invalid/risky/unknown): MX, SMTP, catch-all, disposable. Free agent key.

MCP Server: com.mailtester/email-verification

This MCP server verifies email addresses by checking MX records, attempting SMTP verification, and evaluating whether an address is a catch-all, disposable, or otherwise categorized as valid, invalid, risky, or unknown. It provides a free agent key.

🛠️ Key Features

Email verification outcomes: valid, invalid, risky, unknown
Checks include MX and SMTP verification
Detects catch-all and disposable email status
Requires a free agent key

🚀 Use Cases

Determine whether an email address is deliverable or not
Identify risky or uncertain email addresses
Filter disposable or catch-all addresses during signup or onboarding

⚡ Developer Benefits

Consistent verification categories: valid/invalid/risky/unknown
Supports MX + SMTP-based verification
Focused tool for email validity evaluation

⚠️ Limitations

Verification is limited to the stated checks and categorizations (MX, SMTP, catch-all, disposable).

Topics

ai-agentsemail-verificationmcpmcp-servermodel-context-protocol

Captured live from the server via tools/list.

get_api_key

Get a free API key for this server (no account needed; 25 email verifications per day). Returns the key once — reconnect with 'Authorization: Bearer <api_key>' to use the other tools.

Parameters3

name	string	optional	Your agent's name.
purpose	string	optional	What you verify emails for.
contact	string	optional	Optional operator email or URL.

Raw schema

{
  "type": "object",
  "properties": {
    "name": {
      "type": "string",
      "description": "Your agent's name."
    },
    "purpose": {
      "type": "string",
      "description": "What you verify emails for."
    },
    "contact": {
      "type": "string",
      "description": "Optional operator email or URL."
    }
  }
}

get_credit_balance

Get the current credit balance and a short usage summary for the account.

Parameters

No parameters.

Raw schema

{
  "type": "object",
  "properties": {},
  "required": []
}

list_lists

List the user's bulk verification lists/jobs, most recent first.

Parameters1

limit

integer

optional

Maximum number of lists to return.

Raw schema

{
  "type": "object",
  "properties": {
    "limit": {
      "type": "integer",
      "minimum": 1,
      "maximum": 100,
      "default": 25,
      "description": "Maximum number of lists to return."
    }
  },
  "required": []
}

get_list

Get the details of a single bulk verification list by its id.

Parameters1

list_id

integer

required

The id of the bulk verification list.

Raw schema

{
  "type": "object",
  "properties": {
    "list_id": {
      "type": "integer",
      "description": "The id of the bulk verification list."
    }
  },
  "required": [
    "list_id"
  ]
}

explain_result

Explain what a verification status or reason means in plain English, with a send recommendation. Covers valid, invalid, catch-all/accept-all, unknown, greylisted, disposable, role, free, spam-trap, abuse, do-not-mail, no-mx, disabled, and network. Use when a user asks what a result means.

Parameters1

term

string

required

The status/reason to explain, e.g. 'catch-all', 'GREYLISTED', 'unknown', 'role'. Case-insensitive.

Raw schema

{
  "type": "object",
  "properties": {
    "term": {
      "type": "string",
      "description": "The status/reason to explain, e.g. 'catch-all', 'GREYLISTED', 'unknown', 'role'. Case-insensitive."
    }
  },
  "required": [
    "term"
  ]
}

verify_email

Verify the deliverability of a single email address. Returns a verdict (valid, invalid, risky, unknown). Costs 1 credit.

Parameters1

string

required

The email address to verify.

Raw schema

{
  "type": "object",
  "properties": {
    "email": {
      "type": "string",
      "description": "The email address to verify."
    }
  },
  "required": [
    "email"
  ]
}

verify_batch

Verify a batch of email addresses (up to 25 per call with an agent key). Returns per-email verdicts and saves a list. Costs 1 credit per email.

Parameters2

emails	array	required	Email addresses to verify.
name	string	optional	Optional label for the saved list.

Raw schema

{
  "type": "object",
  "properties": {
    "emails": {
      "type": "array",
      "items": {
        "type": "string"
      },
      "description": "Email addresses to verify."
    },
    "name": {
      "type": "string",
      "description": "Optional label for the saved list."
    }
  },
  "required": [
    "emails"
  ]
}

estimate_cost

Estimate the credit cost of a verification before running it, and whether the user can afford it. Provide either a count of emails, a list_id to re-verify, or an operation ('single'/'finder'). Always quote this before proposing anything billable.

Parameters3

emails	integer	optional	Number of emails to verify (1 credit each).
list_id	integer	optional	Estimate re-verifying an existing list by its id.
operation	string	optional	Operation type: bulk/single (1 credit) or finder (3 credits).

Raw schema

{
  "type": "object",
  "properties": {
    "emails": {
      "type": "integer",
      "description": "Number of emails to verify (1 credit each)."
    },
    "list_id": {
      "type": "integer",
      "description": "Estimate re-verifying an existing list by its id."
    },
    "operation": {
      "type": "string",
      "enum": [
        "bulk",
        "single",
        "finder"
      ],
      "default": "bulk",
      "description": "Operation type: bulk/single (1 credit) or finder (3 credits)."
    }
  }
}

get_batch_status

Get the progress and status of a bulk verification list/job by id.

Parameters1

list_id

integer

required

Raw schema

{
  "type": "object",
  "properties": {
    "list_id": {
      "type": "integer"
    }
  },
  "required": [
    "list_id"
  ]
}

README.md3 KBView on GitHub

MailTester MCP server — email verification for AI agents

Remote Model Context Protocol server that tells an AI agent whether an email address can receive mail before anything is sent to it.

Endpoint: https://app.mailtester.com/mcp (Streamable HTTP, JSON responses)
Official MCP Registry: com.mailtester/email-verification
Website: https://mailtester.com
Agent docs: https://app.mailtester.com/agent-gateway · OpenAPI · llms.txt · agent card

The server is hosted; there is nothing to install. This repository documents how to connect.

Get a key (no account needed)

Connect without a key and call the get_api_key tool, or:

bash

curl -X POST https://app.mailtester.com/agent-gateway/register \
  -H 'Content-Type: application/json' \
  -d '{"name":"my-agent","purpose":"verify signup emails"}'

The key is shown once. Each key gets 25 free verifications per day (unused credits do not roll over) and expires after 30 days; register again when it does. Send it as Authorization: Bearer <api_key>.

Connect

Claude Code

bash

claude mcp add --transport http mailtester https://app.mailtester.com/mcp --header "Authorization: Bearer YOUR_KEY"

Claude Desktop / Cursor / VS Code (mcp.json-style config)

json

{
  "mcpServers": {
    "mailtester": {
      "type": "http",
      "url": "https://app.mailtester.com/mcp",
      "headers": { "Authorization": "Bearer YOUR_KEY" }
    }
  }
}

Tools

Tool	What it does
`get_api_key`	Get a free key (works without a key)
`verify_email`	Verify one address → `valid`, `invalid`, `risky` or `unknown` (1 credit)
`verify_batch`	Verify up to 25 addresses per call, with per-address verdicts
`get_batch_status`, `list_lists`, `get_list`	Follow saved verification lists
`explain_result`	Explain a verdict in plain English, with a send recommendation
`estimate_cost`, `get_credit_balance`	Check credits before running

Verdicts

valid: the mailbox exists and accepts mail
invalid: the address or domain cannot receive mail
risky: accept-all (catch-all) domain, role or disposable address, or a Microsoft 365 address the mail server couldn't confirm
unknown: the receiving server gave no definitive answer

Limits

10 requests per minute per key, one request in flight per key, and a shared daily capacity for free agent keys (HTTP 429 until 00:00 UTC when it is used up). Inbox placement, blacklist monitoring and email finder need a full account at https://mailtester.com.

REST API

The same key works on the REST API: POST https://app.mailtester.com/api/v1/verify, POST https://app.mailtester.com/api/v1/verify/batch, GET https://app.mailtester.com/api/v1/credits. See the OpenAPI description.

Install

Tools (9)

get_api_keyget_credit_balancelist_listsget_listexplain_resultverify_emailverify_batchestimate_cost

Remote endpoint

Streamable HTTP

Hosted server - connect over the network, no local install.

url

https://app.mailtester.com/mcp

Add to VS Code Add to Cursor

claude_desktop_config.json

json

{
  "mcpServers": {
    "email-verification": {
      "command": "npx",
      "args": [
        "-y",
        "mcp-remote",
        "https://app.mailtester.com/mcp"
      ]
    }
  }
}

Desktop config is stdio-only; this bridges via mcp-remote. Native remote: Settings > Connectors.

MCP Server: com.mailtester/email-verification

🛠️ Key Features

🚀 Use Cases

⚡ Developer Benefits

⚠️ Limitations

Topics

get_api_key

get_credit_balance

list_lists

get_list

explain_result

verify_email

verify_batch

estimate_cost

get_batch_status

MailTester MCP server — email verification for AI agents

Get a key (no account needed)

Connect

Tools

Verdicts

Limits

REST API

Install

Remote endpoint

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