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). DNS cannot list DKIM selectors, so when none of the common selectors is found the result says so and a known selector (the s= value in a DKIM-Signature header) can be passed in. Accepts a domain, an email address or a URL. Results are cached for 5 minutes; pass fresh=true right after the user changes DNS.