MailTester Email Verification

com.mailtesterv1.0.1Updated Oct 9, 2026

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

VerifiedStreamable HTTPWeb executableBusiness & CommerceCommunication & Collaboration

Overview

AI-generated overview

Lets an assistant check whether an email address can receive mail, returning valid, invalid, risky or unknown verdicts.

What it does
A hosted MCP server for email verification. Tools include verify_email for a single address, verify_batch for up to 25 addresses per call, get_api_key to obtain a free key, explain_result for a plain-English verdict with a send recommendation, and estimate_cost, get_credit_balance, get_batch_status, list_lists and get_list for credits and saved lists. Verdicts cover MX, SMTP, catch-all, role and disposable checks.
When to use it
Useful before sending mail or accepting signups, when an assistant should confirm an address is deliverable rather than guess. Also handy for cleaning a list of addresses in batches and for explaining why an address was flagged.
Requirements
Remote hosted endpoint; nothing to install. A key is required and is sent as the Authorization header in the form Bearer ; get one with the get_api_key tool or the registration endpoint, no account needed. Network access to the provider is required.
Before you install
The Authorization header carries a secret API key; the key is shown once, expires after 30 days, and free keys allow 25 verifications per day with a shared daily capacity and rate limits. Verification sends the addresses you submit to a third-party service, so treat them as data leaving your environment. Batch calls consume one credit per address.

Installation

In SourceWeft

  1. Open MailTester Email Verification in the dashboard and add it to a workspace.
  2. Enable the server for the chats that should use its tools.

Web executable via Streamable HTTP. Remote servers run from the web runtime once configured in a workspace.

Other MCP clients

Add this to your client's mcpServers config.

{
  "mcpServers": {
    "email-verification": {
      "type": "http",
      "url": "https://app.mailtester.com/mcp"
    }
  }
}

README

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.

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

ToolWhat it does
get_api_keyGet a free key (works without a key)
verify_emailVerify one address → valid, invalid, risky or unknown (1 credit)
verify_batchVerify up to 25 addresses per call, with per-address verdicts
get_batch_status, list_lists, get_listFollow saved verification lists
explain_resultExplain a verdict in plain English, with a send recommendation
estimate_cost, get_credit_balanceCheck 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.

Source: README.md at commit 3bc86f2

Tools

0
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Version history

1
  1. v1.0.1LatestOct 9, 2026