Check every sending domain’s deliverability setup, free.
Paste up to 15 domains to see live MX, SPF, DKIM, DMARC and blocklist status — 5 checks each — the same DNS checks WarmHawk runs continuously on every domain inside the paid dashboard, exposed here as a free public tool. The SPF check also counts what the record costs against the limit of 10 DNS lookups RFC 7208 sets, which is the usual reason a record that looks fine has quietly stopped working. It also explains the RFC 8058 one-click List-Unsubscribe requirement, though that one can’t be verified from a bare domain — it lives on your sent messages, not in DNS, so connect the domain inside WarmHawk to check it on real sends.
Questions
SPF, DKIM, DMARC & List-Unsubscribe FAQ
What is SPF/DKIM/DMARC and why do they matter?+
SPF, DKIM, and DMARC are the three DNS records receiving mail servers check to decide whether your email is legitimate. SPF authorizes sending servers, DKIM signs messages so they can’t be tampered with, and DMARC tells receivers what to do when the first two fail. Missing or misconfigured records are one of the most common reasons cold email lands in spam.
What is RFC 8058 List-Unsubscribe and why does Gmail care about it?+
RFC 8058 defines a one-click unsubscribe header that lets a mailbox provider unsubscribe a recipient with a single request, no login or landing page required. As of November 2025, Gmail and Yahoo escalated enforcement from throttling to outright rejecting bulk mail that lacks it, so this is no longer optional for any sender at volume.
How often should I check my sending domain?+
DNS records and blocklist status can change without any action on your part — a DKIM key rotation, a DNS provider migration, or a single spam complaint can knock a domain out of compliance overnight. Check before starting any new sending domain, and re-check anytime deliverability drops unexpectedly.
Is this the same check WarmHawk runs continuously for paying customers?+
Yes — same underlying SPF/DKIM/DMARC and blocklist logic. The difference is that this free tool gives you a one-time snapshot, while the paid WarmHawk dashboard runs the identical checks continuously against every sending domain you own and alerts you the moment one starts failing. List-Unsubscribe is the one thing neither the tool nor the dashboard can check from DNS — it is a header on a sent message, so WarmHawk instead injects it on every send rather than monitoring it.