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Use when the user asks why their email goes to spam, whether their domain is set up to send email, or before they launch a newsletter, cold outreach, transactional email or a new sending service, e.g. "why are my emails going to spam?", "is my SPF/DKIM/DMARC right?", "do I meet Gmail and Yahoo's sender requirements?" or "I added SendGrid, did I break SPF?". Reads public DNS (DNS-over-HTTPS) and checks: SPF (exactly one record, every include followed and DNS lookups counted per RFC 7208 against the limit of 10, void lookups, loops, +all/?all, ptr), DMARC (RFC 7489 syntax, policy, pct, alignment, inherited from the parent domain, and whether an external report address authorized it), DKIM (17 common selectors plus any you pass; key type and RSA key size read from the key, revoked or broken keys), and MX (provider, null MX). Returns a grade A-F, a verdict, each check with status pass/warn/fail/info, whether the Gmail, Yahoo and Outlook.com sender rules are met, and copy-ready DNS records to fix problems (e.g. one merged SPF record, a starter DMARC record). Use the real result instead of guessing from memory; DNS cannot list DKIM selectors, so if none is found ask for the provider's selector (the s= value in a DKIM-Signature header) and check again. Accepts a domain, an email address or a URL. Results are cached for 5 minutes; pass fresh=true right after the user changes DNS.

Use when you or the user are about to publish or edit an SPF, DMARC or DKIM TXT record, for example after writing a new SPF record that adds a sending service, or when the user pastes a record and asks "is this right?". Detects the record type. SPF: syntax per RFC 7208, every include and redirect followed live in DNS and counted against the 10-lookup limit, void lookups, loops, the final all; returns a lookup tree. DMARC: RFC 7489 tags and values (p, sp, pct, rua/ruf, adkim/aspf, fo). DKIM: key type and RSA key size read from the key, revoked (empty p=) or truncated keys. Returns valid true/false, errors, warnings and where to publish it. Pass domain so a/mx terms without a value can be resolved.