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:
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
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)
{
"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 mailinvalid: the address or domain cannot receive mailrisky: accept-all (catch-all) domain, role or disposable address, or a Microsoft 365 address the mail server couldn't confirmunknown: 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.