Before a browser can load your site, it has to translate your domain name into a server address through DNS — and before an email can reach your inbox, it has to look up which mail server should receive it. This module checks that both of those lookups are configured correctly and redundantly, so a single point of failure can't take your whole domain offline.
| Element | Plain English |
|---|---|
| IPv4/IPv6 resolution | Whether your domain resolves correctly on both the older IPv4 address system and the newer IPv6 system — increasingly relevant as more networks and mobile carriers default to IPv6. |
| DNS redundancy | Whether your domain has multiple nameservers, so if one goes down or becomes unreachable, the others keep your site resolving. |
| MX records | The DNS records that tell the internet which server handles email for your domain, and in what priority order. |
| MX redundancy | Whether you have more than one mail server listed, so a single mail server outage doesn't bounce all your incoming email. |
| Reverse DNS (PTR) | Whether your server's IP address has a matching reverse-lookup record — missing this genuinely hurts email deliverability, since many spam filters check for it. |
| CNAME record | Informational — whether your domain is an alias pointing at another hostname (common for subdomains hosted on a CDN or SaaS platform). Neither good nor bad on its own. |
A domain with only a single nameserver, missing IPv6 support, or no backup mail server usually works fine day-to-day — until that one nameserver has an outage, or a spam filter silently drops your email because of a missing PTR record. These are exactly the kind of quiet, rarely-tested weaknesses that only surface at the worst possible moment.
Most reputable DNS providers (Cloudflare, Route 53, your registrar's built-in DNS) already provide multiple redundant nameservers by default — this is usually a configuration check rather than something to build yourself. IPv6 support depends on your hosting provider. Reverse DNS (PTR) usually has to be requested from whoever owns the IP block — your hosting provider or ISP, not your DNS provider.
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