postbox-tools

Free email checks: 24 blacklists, spoofing/BEC grade, redirect tracing, email spam test, WHOIS.

CommunityOnlineNo sign-inGlobalFreeCan modify data

What it can do

    What data it sees

    Do you need an account

    No: the server works without sign-in

    Free email checks: 24 blacklists, spoofing/BEC grade, redirect tracing, email spam test, WHOIS.

    How to connect

    How to connect postbox-tools to Claude

    The server address to paste into Claude settings:

    https://mcp.postboxservices.com/mcp

    1. Open Claude (claude.ai or the desktop app).
    2. Go to Settings → Connectors.
    3. Click Add custom connector.
    4. Paste the server address copied below into Remote MCP server URL and click Add.
    5. In a chat, click + → Connectors and switch the new connector on.

    Custom connectors are available on Free, Pro, Max, Team and Enterprise plans (Free is limited to one). On Team and Enterprise an organization Owner adds the connector first under Organization settings → Connectors.

    Authorization

    After you click Add, a sign-in window for the service opens. Sign in with your own account and approve access. Claude never sees your password.

    How to connect postbox-tools to ChatGPT

    The server address to paste into ChatGPT settings:

    https://mcp.postboxservices.com/mcp

    1. Open ChatGPT in a browser (chatgpt.com). A Plus, Pro, Business, Enterprise or Edu plan is required.
    2. Turn on developer mode once: Settings → Apps → Advanced settings → Developer mode.
    3. Open Settings → Connectors and click Create.
    4. Fill in the form: Name (anything), Description (one line about what the service does), MCP server URL (copy it below).
    5. Under Authentication choose OAuth if the service requires sign-in, otherwise None. Click Create.
    6. In a new chat open + → Apps/Connectors and enable the connector.

    OpenAI has renamed this section before (Connectors → Apps/Plugins). If the label differs, search settings for "developer mode". On Business/Enterprise workspaces an admin must allow custom connectors first.

    Authorization

    On first use ChatGPT opens the service's sign-in window. Sign in and approve access.

    How to connect postbox-tools to Cursor

    The server address to paste into Cursor settings:

    https://mcp.postboxservices.com/mcp

    Fastest: click Open in Cursor below and confirm the prompt.

    Manually:

    1. In Cursor open Settings → Cursor Settings → MCP and click Add new global MCP server.
    2. Paste the JSON copied below into ~/.cursor/mcp.json (per project: .cursor/mcp.json in the repo root).
    3. Save the file. The server appears in the MCP list; authorize it there if asked.

    Authorization

    If the service needs sign-in, an authorize button appears next to the server in the MCP list.

    Server tool list (8)

    Raw names from tools/list. Only developers need these.

    check_blacklistCheck a domain against domain blacklists (Spamhaus DBL, SURBL, URIBL and others), or an IP address against 24 IP blacklists including Spamhaus ZEN, Barracuda and SpamCop. Checks the exact target given: domains are not resolved to IPs. Returns per-list listing status.
    check_spoofabilityGrade how exposed a domain is to email spoofing and business email compromise, from its public DNS (SPF, DMARC policy strength, alignment, live lookalike domains). Returns an A-F grade with findings.
    trace_redirectFollow a URL server-side through every HTTP redirect hop to its real final destination - per-hop status, IP, TLS and timing, plus phishing/deliverability flags (cross-domain jumps, https downgrades, meta/JS redirects). Fetching is SSRF-hardened (private ranges blocked, HTTPS-only, per-hop validation); how it works: https://redirect.postboxservices.com/
    create_mailtestCreate a disposable test address for a full email deliverability audit (score /10: SPF, DKIM, DMARC + alignment, blacklists, reverse DNS, SpamAssassin content, Gmail/Yahoo bulk-sender compliance). The USER must then send an email from the system they want to test to the returned address, after which get_mailtest_result returns the score.
    get_mailtest_resultFetch the score and breakdown of a mail test created with create_mailtest, once the user has sent their email to the disposable address.
    analyze_emlRun a deliverability/content analysis on a raw RFC 822 email (.eml source: full headers + body). IMPORTANT LIMITS: with no live SMTP session, SPF, blacklist and reverse-DNS cannot be verified from a file - for the authoritative score use create_mailtest instead.
    get_domain_ageGet a domain's registration date and age (young domains have weak sending reputation).
    whois_lookupWHOIS summary for a domain: registrar, created/updated/expires dates, nameservers, DNSSEC, status flags.