# Mail Domain Check > Mail Domain Check is a bilingual public email-authentication diagnostic service for MX, SPF, DKIM, DMARC, PTR, MTA-STS, TLS-RPT, and CAA. It provides a free summary API and CLI plus an automated paid report with complete evidence and remediation actions. No customer login or mailbox access is required. Diagnostics use public DNS, an optional public sending IP, and public HTTPS policy files. Free analytics retain irreversible hashes and aggregate metrics, not raw domains or sending IPs. Results do not guarantee inbox placement and do not replace a complete security or compliance audit. The public scan API is rate-limited to interactive diagnostics. Cross-origin browser calls are not supported; use the same-origin scanner, the published Node.js CLI, or a server-side HTTP client. The free response intentionally omits complete evidence and remediation actions. ## Developer documentation - [Developer overview](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/developers/): Choose the browser scanner, dependency-free CLI, or public HTTP API. - [API documentation](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/developers/api/index.html.md): Markdown reference for requests, responses, privacy, and rate limits. - [OpenAPI 3.1.2 description](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/openapi.json): Machine-readable contract for the public scan and health endpoints. - [CLI documentation](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/developers/cli/index.html.md): Markdown reference for terminal use, selectors, sending IPs, JSON, and privacy. - [CLI source](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/cli/mail-domain-check.mjs): MIT-licensed single-file Node.js 20+ client with no package dependencies. ## Product - [English scanner](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/en/?utm_source=llms): Interactive free summary and automated complete-report purchase. - [Chinese scanner](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/?utm_source=llms): 中文免费摘要与自动完整报告。 - [SMTP error decoder](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/tools/smtp-error-decoder/): Local-only parser for three-digit SMTP replies, enhanced status codes, Gmail-specific branches, and exact repair-guide routing. - [Email authentication header analyzer](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/tools/email-header-analyzer/): Local-only parser for receiver-reported SPF, DKIM, DMARC, ARC, visible From, signing identities, and alignment evidence. - [Email sender inventory builder](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/tools/email-sender-inventory/): Local-only inventory for message streams, visible From domains, providers, owners, DKIM identities, Return-Path domains, receiver evidence, and DMARC rollout gaps, with bounded CSV and JSON export. - [SPF lookup counter](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/tools/spf-lookup-counter/): Live public-DNS check for SPF record count, observed DNS-causing terms, the 10-term limit, and incomplete include or redirect chains. - [DKIM selector checker](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/tools/dkim-selector-checker/): Exact live-DNS lookup for a known d= domain and s= selector, with safe key type, publication, revocation, service, hash, and flag metadata. - [DMARC policy checker](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/tools/dmarc-policy-checker/): Current RFC 9989 bounded DNS Tree Walk with direct-record count, inherited p/sp/np policy, alignment modes, aggregate-reporting state, test mode, and conflict detection. - [MTA-STS policy checker](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/tools/mta-sts-checker/): Live RFC 8461 STSv1 announcement and fixed-path HTTPS policy check with safe mode, max_age, MX-pattern-count, and companion TLS-RPT diagnostics. - [DMARC record generator](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/tools/dmarc-record-generator/): Local-only current RFC 9989 builder for p, sp, np, alignment, aggregate and failure reporting, and t=y; historic pct, rf, and ri tags are deliberately excluded. - [DMARC report analyzer](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/tools/dmarc-report-analyzer/): Local-only RFC 9990 and legacy aggregate XML or XML.GZ reader with weighted alignment, sending-source, policy, duplicate, and CSV summaries. - [Reverse DNS and PTR checker](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/tools/reverse-dns-checker/): Live IP-only PTR lookup with bounded A or AAAA forward confirmation for Gmail 5.7.25 and 4.7.23 troubleshooting; raw hostnames and DNS answers stay out of the free result. - [Payment and report recovery](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/en/help/): Exact Base USDC parameters, private recovery-link behavior, and irreversible-payment boundaries. ## Diagnostic guides - [Email authentication guide index](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/guides/): SPF, DKIM, DMARC, PTR, MTA-STS, provider requirements, and exact SMTP rejection codes. - [Web3 email security check](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/guides/web3-email-security/): Authentication and anti-spoofing review for wallet alerts, governance notices, transactional email, and newsletters, with Base USDC report delivery. - [Crypto phishing email header check](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/guides/crypto-phishing-email-header-check/): Private workflow for suspicious wallet alerts, exchange notices, DAO messages, and token emails using authentication, identity-alignment, and Received-routing evidence. - [SPF 10-query limit](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/guides/spf-10-lookup-limit/): Static lookup-budget interpretation and safe remediation boundaries. - [DKIM selector discovery](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/guides/dkim-selector/): Why DKIM cannot be judged reliably without a real selector. - [DMARC policy discovery](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/guides/no-dmarc-record-found/): RFC 9989 direct lookup and bounded parent-domain tree walk. - [PTR and forward DNS](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/guides/gmail-550-5-7-25-ptr-record/): Actual sending-IP reverse and forward confirmation. ## Optional - [Chinese payment help](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/help/): 中文付款、恢复和数据边界。 - [Sitemap](https://mail-domain-check-zac2.coral-ibis-2405.chatgpt.site/sitemap.xml): Complete canonical human-readable page list.