MailTester MCP server

Endpoint: https://app.mailtester.com/mcp · Authentication: No auth

Verify email addresses and inspect deliverability signals through MailTester.

Test it live Run the release-readiness report

How do I authenticate?

Add the endpoint directly in your client. The catalog records no authentication requirement; no OAuth sign-in or API key is configured in this setup. The live server may change.

Authentication and connection guide

Connection specification

Remote endpoint: https://app.mailtester.com/mcp
Browser access: Not yet measured
Declared MCP transport: Streamable HTTP
Live-validated MCP transport: Streamable HTTP — Observed by the latest catalog validation
Declared authentication: No authentication
Detected authentication: No authentication detected or retained from publisher evidence
Alternative authentication: API key
Protocol lifecycle: Stateful MCP · 2024-11-05
Required header: Authorization — Optional credential alternative to public access.
Category: Communication

Product documentation · Source repository · Official listing documentation · Official MCP Registry record

Provider guidance

Keyless verification has a small shared trial allowance. Register through the publisher for a private API key and account quota.

More Communication MCP servers · Browse all MCP servers · Test this endpoint in the MCP Playground

Authorization setup

No app registration needed

This catalog entry does not require authorization or provider app registration.

Connect it

Live-validated endpoint: https://app.mailtester.com/mcp · Streamable HTTP. No authentication is required by the catalog listing.

Agent prompt for Claude Code or Codex

Add the MailTester MCP server to my MCP client configuration and verify that it works.

What it is: Verify email addresses and inspect deliverability signals through MailTester.
Server URL: https://app.mailtester.com/mcp
Transport: Streamable HTTP (remote MCP server, no local install).
Authentication: none. The server accepts connections without credentials.
Tools (9, as last observed by mcptest): estimate_cost, explain_result, get_api_key, get_batch_status, get_credit_balance, get_list, list_lists, verify_batch, verify_email.
Reference: https://mcptest.io/servers/mailtester/

Steps:
1. Work out which MCP client I use (Claude Code, Codex, Cursor, VS Code or another) and add the server under the name "mailtester" in that client's MCP configuration, user scope unless I ask otherwise.
   Claude Code: claude mcp add --transport http --scope user 'mailtester' 'https://app.mailtester.com/mcp'
   Codex: codex mcp add 'mailtester' --url 'https://app.mailtester.com/mcp'
   Other clients: use the setup for that client on the reference page.
2. Never write a credential value into a file that could be committed; reference an environment variable or the client's secret store, and ask me for any value you need.
3. Verify: connect to the server and call tools/list. Confirm the tools above are listed, and report any sign-in step I still have to complete.

Claude Code setup

Run in a terminal. This user-scoped entry is available across projects.

claude mcp add --transport http --scope user 'mailtester' 'https://app.mailtester.com/mcp'

Codex CLI setup

Run in a terminal; Codex stores the entry in ~/.codex/config.toml.

codex mcp add 'mailtester' --url 'https://app.mailtester.com/mcp'

Cursor setup

Add to .cursor/mcp.json for this project, or ~/.cursor/mcp.json for all projects.

{
  "mcpServers": {
    "mailtester": {
      "url": "https://app.mailtester.com/mcp"
    }
  }
}

VS Code setup

Add to .vscode/mcp.json, or run “MCP: Open User Configuration” for a private user-level entry.

{
  "servers": {
    "mailtester": {
      "type": "http",
      "url": "https://app.mailtester.com/mcp"
    }
  }
}

Claude setup

Add the endpoint above in Claude:

Customize > Connectors > Add custom connector
Team/Enterprise: Organization settings > Connectors > Add > Custom > Web

Claude Desktop setup

Add the endpoint above in Claude Desktop:

Remote: Customize > Connectors (same as claude.ai)
Local: Settings > Developer > Edit Config, or Settings > Extensions for .mcpb files
~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows), local servers only

ChatGPT setup

Add the endpoint above in ChatGPT:

ChatGPT web: Plugins > Add custom MCP server, then configure authentication and accept the risk warning

Windsurf setup

Add the endpoint above in Windsurf:

~/.config/devin/mcp_config.json (%APPDATA%\devin\mcp_config.json on Windows), serverUrl or url
Cascade panel > ... > MCPs > Open MCP config file

Gemini CLI setup

Add the endpoint above in Gemini CLI:

gemini mcp add --transport http <name> <url>
~/.gemini/settings.json (user) or .gemini/settings.json (project), mcpServers

MCP SDK setup

Add the endpoint above in MCP SDK:

Programmatic: new Client(...).connect(new StreamableHTTPClientTransport(url))

Notes for every client

Optional api key alternative: Store MAILTESTER_API_KEY in your operating system keychain, secret manager, or protected environment; never commit the value. The Authorization header syntax is Bearer <MAILTESTER_API_KEY>.
Provider guidance: Keyless verification has a small shared trial allowance. Register through the publisher for a private API key and account quota.

Client compatibility

Client	Status	Why
Claude Code	Supported	Claude Code supports Streamable HTTP servers and servers without authentication or API key headers.
Codex	Supported	Codex supports Streamable HTTP servers and servers without authentication or API key headers.
Cursor	Supported	Cursor supports Streamable HTTP servers and servers without authentication or API key headers.
VS Code	Supported	VS Code supports Streamable HTTP servers and servers without authentication or API key headers.
Claude	Supported	Claude supports Streamable HTTP servers and servers without authentication or API key headers.
Claude Desktop	Supported	Claude Desktop supports Streamable HTTP servers and servers without authentication or API key headers.
ChatGPT	Partial	Stateful routing needs operational care: ChatGPT can preserve MCP sessions, but the deployment must route a session consistently and retain its state.
Windsurf	Supported	Windsurf supports Streamable HTTP servers and servers without authentication or API key headers.
Gemini CLI	Supported	Gemini CLI supports Streamable HTTP servers and servers without authentication or API key headers.
MCP SDK	Supported	MCP SDK supports Streamable HTTP servers and servers without authentication or API key headers.

Computed from this server's validated transport, protocol and authentication against documented client support. Checks the catalog has not observed are not counted.

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Guides for this server

Watch this server for breaking changes

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Latest validation evidence

Validation status: Online when last tested
Validation checked at: Oct 26, 2026 at 11:07 AM
Validation detail: Negotiated stateful MCP 2024-11-05 at https://app.mailtester.com/mcp; detected transport streamable-http; authentication none

Tool inventory

What the catalog validator observed on Oct 26, 2026 at https://app.mailtester.com/mcp without credentials. The live server may have changed since; connect in the Playground for the current list.

Tools provided by MailTester 9

Some details were sanitized for public display.

estimate_costNo outputSchema
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.
Input emails?: integer, list_id?: integer, operation?: string
- emails?: integeroptional
  Number of emails to verify (1 credit each).
- list_id?: integeroptional
  Estimate re-verifying an existing list by its id.
- operation?: stringoptional
  Operation type: bulk/single (1 credit) or finder (3 credits).
explain_resultNo outputSchema
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.
Input term: string
- term: stringrequired
  The status/reason to explain, e.g. 'catch-all', 'GREYLISTED', 'unknown', 'role'. Case-insensitive.
get_api_keyNo outputSchema
Get your own free API key for this server (no account needed; 25 email verifications per day). Optional: the verification tools already work without a key on a shared trial. Returns the key once — reconnect with 'Authorization=[REDACTED] <api_key>' for your own quota and the list tools.
Input contact?: string, name?: string, purpose?: string
- contact?: stringoptional
  Optional operator email or URL.
- name?: stringoptional
  Your agent's name.
- purpose?: stringoptional
  What you verify emails for.
get_batch_statusNo outputSchema
Get the progress and status of a bulk verification list/job by id.
Input list_id: integer
- list_id: integerrequired
get_credit_balanceNo outputSchema
Get the current credit balance and a short usage summary for the account.
Input No parameters
get_listNo outputSchema
Get the details of a single bulk verification list by its id.
Input list_id: integer
- list_id: integerrequired
  The id of the bulk verification list.
list_listsNo outputSchema
List the user's bulk verification lists/jobs, most recent first.
Input limit?: integer
- limit?: integeroptional
  Maximum number of lists to return.
verify_batchNo outputSchema
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.
Input emails: array, name?: string
- emails: arrayrequired
  Email addresses to verify.
- name?: stringoptional
  Optional label for the saved list.
verify_emailNo outputSchema
Verify the deliverability of a single email address. Returns a verdict (valid, invalid, risky, unknown). Costs 1 credit.
Input email: string
- email: stringrequired
  The email address to verify.