Connect CheckMX.

Verify emails and review your campaigns, mailboxes and deliverability from your AI assistant, read-only. Or call the API from your application.

Connect an assistant

Copy this URL into your AI app’s connector settings. Choose OAuth (browser sign-in) when available. CheckMX’s connector is read-only: it can look things up and verify addresses, but it cannot change anything in your account.

https://checkmx.dev/mcp

In Claude on the web or desktop, open connector settings and add a custom connector named CheckMX.
Paste the connection URL from the box above and choose OAuth or browser sign-in.
Sign in to CheckMX with Google, review the permissions and approve the connection.
Enable verify_email and ask Claude to check an address you are authorized to verify. If OAuth is unavailable, use the API key guide in the last tab with a client that accepts headers.

In ChatGPT’s app settings, add a custom MCP app named CheckMX.
Paste the connection URL from the box above and choose OAuth.
Sign in to CheckMX with Google, review the permissions and approve access.
Enable the app in your chat and ask it to use verify_email. If OAuth is unavailable, use the API key guide with a client that accepts headers.

Open Cursor’s MCP settings and add CheckMX to your user MCP configuration using the example below.
Save the configuration and enable the CheckMX server.
Complete browser sign-in with Google and approve access. If browser sign-in is unavailable, add the headers field from the API key example in the last tab.
Ask Cursor to use verify_email for an address you are authorized to check.

{
  "mcpServers": {
    "checkmx": {
      "url": "https://checkmx.dev/mcp"
    }
  }
}

Run these two commands in a terminal. The Codex app uses the same MCP configuration as the Codex CLI. The second command opens browser sign-in.
Sign in to CheckMX with Google and approve access.
To see interactive cards, add the setting below to ~/.codex/config.toml and restart the app. Without it you get the same data as Markdown text.
Ask Codex to use verify_email for an address you are authorized to check, or ask about your campaigns and mailboxes.

codex mcp add checkmx --url https://checkmx.dev/mcp
codex mcp login checkmx

[features]
enable_mcp_apps = true

Run these two commands in your terminal. The second opens browser sign-in.
Sign in to CheckMX with Google and approve access.
Start codex and ask it to use verify_email for an address you are authorized to check. The Codex CLI shows results as Markdown text, not cards.

codex mcp add checkmx --url https://checkmx.dev/mcp
codex mcp login checkmx

Run this command in your terminal.
Start claude, type /mcp, choose checkmx and sign in to CheckMX with Google in your browser.
Ask Claude Code to use verify_email for an address you are authorized to check. Claude Code shows results as Markdown text, not cards.
No browser sign-in? Use the API key guide in the last tab instead.

claude mcp add --transport http checkmx https://checkmx.dev/mcp

Prefer OAuth browser sign-in if your client offers it. Otherwise, sign in to the API Keys dashboard, create a named key and copy it once.
For Cursor, use the configuration below. For another HTTP MCP client, add the same connection URL and set the Authorization header to Bearer YOUR_CHECKMX_API_KEY.
Replace the placeholder with your key in your client’s private configuration or secret storage, then save and enable CheckMX. Keep the key out of chats and shared files.
Confirm verify_email is available and check one address. Revoke the key from API Keys when you no longer need it.

{
  "mcpServers": {
    "checkmx": {
      "url": "https://checkmx.dev/mcp",
      "headers": {
        "Authorization": "Bearer YOUR_CHECKMX_API_KEY"
      }
    }
  }
}

Claude Code HTTP server entry (use your client’s configuration editor):

{
  "mcpServers": {
    "checkmx": {
      "type": "http",
      "url": "https://checkmx.dev/mcp",
      "headers": {
        "Authorization": "Bearer YOUR_CHECKMX_API_KEY"
      }
    }
  }
}

Custom connector availability depends on your assistant’s plan and workspace settings. No source-code download or local server is required.

What your assistant can do

18 read-only tools. Ask in plain language; the assistant picks the tool.

Verify emails: verify_email, check_history, verification_insights. Try “Verify jane@acme.com” or “Show my risky checks from the last 7 days.”
Bulk jobs: list_verification_jobs, get_verification_job. Try “What bulk jobs finished this week?” Uploads happen in the dashboard.
Campaigns: campaign_performance, ab_test_results, campaign_progress, sequence_steps. Try “How did my campaigns do over 30 days?” or “Which sequence step gets the most replies?”
Mailboxes and deliverability: mailbox_performance, mailbox_health, domain_health, inbox_replies. Try “Which mailboxes need attention?” or “Check DNS and blocklists for example.com.”
Contacts and imports: contacts_overview, import_history, suppression_overview. Try “Summarize my contacts and recent imports.”
Access and webhooks: api_keys_overview, webhook_deliveries. Try “Which API keys were used recently?” Key values and signing secrets are never returned.

Where cards show

Results appear as interactive cards in Claude (web and desktop), ChatGPT, Cursor 2.6 or later, VS Code, and the Codex app when enable_mcp_apps = true is set. Codex CLI, Claude Code and other terminal clients get the same data as Markdown text. Card actions such as filters, Refresh, Re-check, Export CSV and Open in CheckMX only re-run read tools or open links.

Permissions and safety

Browser sign-in grants a single OAuth scope, verify. An API key works as a Bearer token if your client cannot sign in.
Everything is read-only. No tool creates, edits, sends, deletes, pauses or launches anything.
verify_email is the only tool that runs a live email check. Repeat checks of the same address within 7 days are cached. Ask your assistant to confirm before it checks many addresses, and only check addresses you are authorized to verify.
Your assistant cannot start bulk jobs, launch campaigns, edit sequences, manage mailboxes, change suppression, or manage keys and webhooks. Make those changes in the dashboard.

Use the API

Sign in to the API Keys dashboard, create a named key and copy it once. Send a POST request to https://checkmx.dev/api/verify with Authorization: Bearer YOUR_CHECKMX_API_KEY, Content-Type: application/json and a JSON body containing email. Keep your key in application secret storage rather than a chat message or shared configuration.

Understand the result

safe: available checks support delivery, without a delivery guarantee.
risky: signals require caution, including catch-all behavior. Catch-all acceptance does not confirm an individual mailbox.
invalid: checks indicate the address is not usable.
unknown: inconclusive, such as a timeout, deferral or rate limit. Do not treat it as invalid.

CheckMX does not send an email message during verification. SMTP servers can withhold or change their responses.

Limits and disconnection

Checks share service-wide SMTP pacing and capacity limits. Bulk jobs accept a CSV up to 2 MB and up to 10,000 unique addresses per job, and may take time to complete. Disconnect an assistant or revoke an API key from API Keys. Once revoked, its credentials stop working.

Support and data handling

Contact hello@checkmx.dev. Read the privacy policy and terms of service before connecting.