Email deliverability check
Type your domain. Stamp reads its SPF, DKIM, DMARC and MX records from live DNS, checks them against the rules Gmail, Yahoo and Outlook enforce, and gives you the exact records to fix what is wrong.
Add these at your DNS host (Cloudflare, GoDaddy, Namecheap, Route 53…). Name is the host field; some hosts want only the part before your domain.
Paste an SPF, DMARC or DKIM record. SPF includes are followed live and counted against the 10-lookup limit, so you know it works before it goes into DNS.
Gmail and Yahoo require SPF or DKIM on every message, and SPF, DKIM and a DMARC record from anyone sending 5,000+ a day. Outlook.com started rejecting non-compliant bulk mail in 2025. Miss one and your mail goes to spam or bounces.
Stamp follows every SPF include and counts DNS lookups the way receivers do (RFC 7208: 10 lookups, 2 void lookups), finds duplicate records, walks DMARC to the parent domain, checks report-address authorization and reads each DKIM key's size.
Each problem comes with the fix: one merged SPF record instead of two, a DMARC record to start monitoring, the next policy step when you are ready. Copy them into your DNS host, wait a few minutes, check again.
Assistants and agents can call Stamp through MCP at https://stamp.clawhard.com/mcp (tools stamp_check_email_domain and stamp_check_dns_record) or the JSON API at /api/v1/check?domain=. They get the same grade, findings and fix records, read from live DNS instead of guessed.
Add Stamp to ChatGPT, Claude, Cursor or any assistant that supports MCP, then ask it to check a domain's SPF, DKIM, DMARC and MX from live DNS, see if it meets the Gmail and Yahoo sender rules, and get the records to fix it. No key, no login.
https://stamp.clawhard.com/mcpclaude mcp add --transport http clawhard-stamp https://stamp.clawhard.com/mcp
Press Add to Claude, or open Customize → Connectors → Add custom connector, paste the URL and leave sign-in empty.
Open Plugins → + → Add custom MCP server, paste the URL, choose No authentication, accept the warning, then Create as a plugin. Start a chat and type @ to use it.
codex mcp add clawhard-stamp --url https://stamp.clawhard.com/mcp
gemini mcp add --transport http clawhard-stamp https://stamp.clawhard.com/mcp
{
"mcpServers": {
"clawhard-stamp": { "url": "https://stamp.clawhard.com/mcp" }
}
}{
"servers": {
"clawhard-stamp": { "type": "http", "url": "https://stamp.clawhard.com/mcp" }
}
}No desktop app? Add to VS Code in the browser · VS Code Insiders · Add to Cursor in the browser
Other apps: Goose · LM Studio. Any MCP client works with the URL (Streamable HTTP, no headers).
OpenAPI (custom GPT Actions, scripts) · llms.txt · MCP server card · Agent card · All Clawhard tools in one connector
Stamp checks a domain's email authentication from live DNS: SPF with the 10-lookup limit, DMARC, DKIM keys and MX. It says whether you meet the Gmail, Yahoo and Outlook sender rules and gives you the exact DNS records to fix what is wrong. No account.
Most often because the domain is missing SPF, DKIM or DMARC, or one of them is broken: two SPF records, more than 10 SPF lookups, or no DMARC record. Gmail and Yahoo require SPF or DKIM on all mail, and SPF, DKIM and DMARC for bulk senders. Stamp checks all of these from live DNS and gives you the records to fix them. Content, sending reputation and blocklists also matter, and Stamp does not check those.
RFC 7208 lets receivers do at most 10 DNS lookups to evaluate an SPF record. Every include, a, mx, ptr, exists and redirect counts, including the ones inside included records. At 11 the result is a permanent error and SPF fails for every message. Stamp counts them and shows the full tree.
No. A domain must publish exactly one TXT record starting with v=spf1. With two, receivers return a permanent error and SPF fails. Merge them into one record; Stamp writes the merged version for you.
Start with p=none and a rua= report address to see who sends mail as your domain without affecting delivery. When the reports show all your real senders passing, move to p=quarantine and then p=reject. p=none meets the Gmail and Yahoo bulk sender minimum but does not stop spoofing.
Since February 2024 everyone sending to Gmail or Yahoo needs SPF or DKIM, and senders of 5,000+ messages a day need SPF, DKIM and a DMARC record (p=none or stricter) with alignment, plus one-click unsubscribe and a low spam rate. Outlook.com began rejecting non-compliant bulk mail in 2025. Stamp checks the DNS parts.
DNS has no way to list DKIM selectors, so a checker has to guess the name. Stamp tries 17 common selectors. Find yours as s= in the DKIM-Signature header of an email you sent, or in your provider's DNS setup page, and add it under "Your provider uses its own DKIM selector?".
Yes. Add the MCP server https://stamp.clawhard.com/mcp (tools stamp_check_email_domain and stamp_check_dns_record), or call GET https://stamp.clawhard.com/api/v1/check?domain=example.com (see /openapi.json). It is also on the Clawhard MCP server at https://mcp.clawhard.com/mcp.
For AI assistants and developers: llms.txt · API (OpenAPI) · MCP server · sitemap