| Check | Frequency | What it catches |
|---|---|---|
| SPF record + recursive DNS-lookup count (RFC 7208 limit 10) + 'all' qualifier | every 6h | Missing/duplicate records, PERMERROR-causing lookup overflows, +all/?all weaknesses |
| DKIM selector probes (your selectors + common defaults) | every 6h | Missing or revoked signing keys |
| DMARC record, policy (p/sp/pct), rua reporting | every 6h | Missing/duplicate/invalid records, monitor-only drift, unprotected subdomains |
| MX, MTA-STS, TLS-RPT presence | every 6h | Reply-path and TLS hardening gaps |
| DNS blocklists (named below) | every 12h | New listings of your domain or its A-record IPs |
| DMARC aggregate (RUA) report analysis (if you route reports to us) | as reports arrive | Sources failing authentication as your domain, unknown senders, alignment drops |
| List | Type | Usage policy |
|---|---|---|
| SpamCop | ip | https://www.spamcop.net/fom-serve/cache/351.html |
| Barracuda | ip | https://barracudacentral.org/rbl/how-to-use |
| SORBS | ip | http://www.sorbs.net/general/using.shtml |
| PSBL | ip | https://psbl.org/ |
| SURBL multi | domain | https://www.surbl.org/usage-policy |
| Tornevall | ip | https://dnsbl.tornevall.org/ |
We name lists precisely instead of claiming "all blacklists." Notably, Spamhaus is not currently included: their public mirrors prohibit commercial query services, and we only query lists in ways their operators permit. Coverage expands as licensing allows.
We cannot see inside Gmail/Outlook filtering, your ESP's shared-IP reputation, content-based filtering, or engagement signals. No placement guarantees, from us or from anyone being honest. What we make visible: the measurable, fixable failures that silently kill deliverability.
Microsoft Outlook high-volume sender requirements (May 2025, 550 5.7.515 rejection): Microsoft Tech Community, techcommunity.microsoft.com. Google & Yahoo bulk-sender authentication requirements (Feb 2024): provider sender guidelines. RFC 7208 (SPF), RFC 6376 (DKIM), RFC 7489 (DMARC).
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