# Domain Mail Check Find out if a domain's email will reach the inbox, and how to fix it. It is free, with no sign-up and no key. ## What it does Check how a domain is set up for email, whether Gmail and Outlook are likely to accept its mail, and who it is registered with, from public DNS, free blocklists and registry data. Ask "will Gmail accept mail from example.com sent from 203.0.113.7?", "is DMARC set up correctly for github.com?", "check SPF and DKIM for example.com", "which mail provider does acme.io use?" or "when does openai.com expire?". The email check reads the domain's SPF record (following include and redirect, counting DNS lookups against the limit of 10), its DMARC policy, the MX records and, when you give a DKIM selector, whether the DKIM key is published. It returns a grade from A to F for protection against spoofing, the problems it found and a short list of fixes. The DNS records tool reads A, AAAA, MX, TXT, CAA and NS records with their TTLs, which also shows which mail provider a domain uses and which certificate authorities may issue for it. The registration tool reads the domain's registry record over RDAP: registrar, creation and expiry dates, status flags and name servers. The delivery check gives one verdict for Gmail and Outlook, the top 3 causes and one fix for each. It tests the published sender rules (SPF listing the sending IP, DKIM, DMARC, reverse DNS of the IP, key length) and reads 6 free blocklists (SpamCop, PSBL, UCEPROTECT level 1, Mailspike and NordSpam for the IP and the domain). Each rule and each list names its official source. The cold-email launch score gives a score from 0 to 100 for a new sending domain, with a verdict of ready, almost or not_ready and the 5 fixes to make first. It tests SPF, DKIM, DMARC, reply mail, a domain blocklist, the domain's age from the registry record and the shape of its name. Each rule names its source and is labelled standard (a published requirement) or opinion (common advice nobody requires, which never decides not_ready). The DNS hygiene check finds 4 faults beyond SPF, DKIM and DMARC: no CAA record (any certificate authority may issue for the domain), DNSSEC that is off or broken, mail servers that do not offer STARTTLS (mail arrives unencrypted), and dangling CNAMEs on 20 common subdomains such as www, shop and help, which point at a name that no longer exists, some of which anyone can register or create. For STARTTLS it reads only the greeting and EHLO answer of up to 2 mail servers and never sends mail; a server it cannot reach is reported as not read, not as a fault. DNS answers come from Cloudflare's DNS over HTTPS service with Google Public DNS as a fallback, and registration data from the registry of the domain's ending, found through IANA's RDAP directory. Every answer names its source and the date it was read. It does not send a test message or read mailboxes, so a good verdict means no published rule is broken, not a promise of the inbox; it does not read sender reputation, discover subdomains beyond a fixed list of common names, or return who owns a domain: registrant and contact details are never read or returned. It checks the exact domain you give, so a parent domain's SPF or DMARC record is not inherited. The domains you ask about are not stored; the only lasting record is a daily count of calls per tool. - Reads a domain's SPF record, counts its DNS lookups and flags weak or broken policies - Reads the DMARC policy, percentage and report address - Checks whether DKIM keys are published for up to 5 selectors you name - Grades email spoofing protection from A to F with a short list of fixes - Reads A, AAAA, MX, TXT, CAA and NS records with TTLs and names the mail provider from the MX records - Shows registrar, creation and expiry dates, status flags and name servers from the registry over RDAP - Never returns registrant or contact details; names its sources and dates - Gives one verdict on whether Gmail and Outlook will likely accept the domain's mail, the top 3 causes and one fix each - Checks SPF for the sending IP, reverse DNS, DKIM key length and DMARC against the Gmail, Yahoo and Outlook rules - Reads 6 free blocklists for the domain and the sending IP, with each list's terms link - Scores a cold-email sending domain 0 to 100 from SPF, DKIM, DMARC, domain age and name, with fixes - Labels each rule standard or opinion and links its source, so advice is not shown as a requirement - Finds a missing CAA record, off or broken DNSSEC, mail servers without STARTTLS and dangling CNAMEs ## Who it is for Anyone who asks an AI assistant a question like this one: “Is DMARC set up correctly for github.com?” Roles that use it at work: Startup founder, IT admin, Deliverability consultant, Sales lead. Role guides that use it: [Startup founder](https://tools.openkrill.app/for/startup-founder). ## Price Domain Mail Check is free to use. There is no sign-up, no account and no API key. Calls are limited to 60 calls a minute per network and 5000 calls a day per server, shared by all callers. Repeat questions are answered from a cache. ## Tools it offers - `launch_score`: Score a cold-email domain - `delivery_check`: Check mail delivery - `check_dns_hygiene`: Check DNS security faults - `check_email_auth`: Check email authentication - `check_dns_records`: Look up DNS records - `lookup_domain_registration`: Look up domain registration ## Connect The MCP server is `https://mailcheck.openkrill.app/mcp` (streamable HTTP). It needs no key. Claude Code, in one command: ``` claude mcp add --transport http mailcheck https://mailcheck.openkrill.app/mcp ``` Hermes Agent, in one command that answers its two setup questions (no key, enable all tools): ``` printf 'n\ny\n' | hermes mcp add mailcheck --url https://mailcheck.openkrill.app/mcp ``` Or add these lines to `~/.hermes/config.yaml`, under an existing `mcp_servers:` key if the file has one. Start a new Hermes session after either step. ``` mcp_servers: mailcheck: url: https://mailcheck.openkrill.app/mcp ``` Any other agent: give it this page's Markdown address, `https://tools.openkrill.app/tools/mailcheck.md`, and ask it to connect Domain Mail Check. Install guides, each checked with a real call: [Domain Mail Check in ChatGPT](https://tools.openkrill.app/integrations/mailcheck/chatgpt), [Domain Mail Check in Claude](https://tools.openkrill.app/integrations/mailcheck/claude), [Domain Mail Check in Cursor](https://tools.openkrill.app/integrations/mailcheck/cursor), [Domain Mail Check in VS Code](https://tools.openkrill.app/integrations/mailcheck/vscode), [Domain Mail Check in Pi](https://tools.openkrill.app/integrations/mailcheck/pi). ## Job recipes for agents Step-by-step recipes that walk an agent through 3 jobs with this server's tools: - Score a cold-email domain, with `launch_score` - Check mail delivery, with `delivery_check` - Check DNS security faults, with `check_dns_hygiene` [Download the recipes as SKILL.md](https://tools.openkrill.app/skills/mailcheck-jobs/SKILL.md). Save it as `mailcheck-jobs/SKILL.md` in your agent's skills folder. A connected MCP client gets the same recipes from `prompts/list` on the gateway, `https://api.openkrill.app/gateway/mcp`. It is listed under Websites, domains and email in the [full tool list](https://tools.openkrill.app/tools). The same facts in plain text are in [llms.txt](https://tools.openkrill.app/llms.txt). Source: the Domain Mail Check listing, version 1.5.0. As of 2026-10-18.