If your website suddenly becomes unreachable or your emails start bouncing back, there’s a good chance the culprit is hiding in your DNS configuration. Domain Name System health isn’t something most people think about until something breaks—and by then, you’re already losing visitors, customers, and revenue. The truth is, DNS problems are remarkably common, yet most organizations only check their DNS settings when they’re actively making changes or dealing with an outage.
I learned this lesson the hard way a few years back when managing a client’s e-commerce site. Everything seemed fine until customers started complaining they couldn’t access the checkout page. After some frantic investigation, I discovered that a subdomain we’d set up for testing months earlier had an outdated A record pointing to a server we’d decommissioned. The DNS entry was still active, causing intermittent routing issues that took down parts of the site randomly. That incident cost the client thousands in lost sales over a weekend, and it could have been prevented with proper DNS monitoring.
Why DNS Health Monitoring Matters
Your DNS is essentially the phonebook of the internet—it translates human-readable domain names into IP addresses that computers can understand. When DNS fails or misconfigures, the results range from minor annoyances to complete service outages. But DNS issues don’t always announce themselves dramatically. Sometimes they lurk in the background, slowly degrading performance, creating security vulnerabilities, or causing sporadic problems that are difficult to diagnose.
The modern web infrastructure is complex. Most organizations don’t just have a single domain pointing to a single server anymore. You’ve got multiple subdomains for different services: mail servers, development environments, staging servers, CDN endpoints, API gateways, and more. Each of these requires proper DNS configuration, and each represents a potential failure point.
Critical DNS Records to Monitor
A and AAAA Records are your basic building blocks—they point your domain to IPv4 and IPv6 addresses respectively. You need to monitor these to ensure they’re pointing to active, functioning servers. I’ve seen countless situations where someone migrated to a new hosting provider, updated the main domain records, but forgot about subdomains that were still pointing to the old infrastructure.
MX Records control your email delivery. If these are misconfigured or pointing to non-existent mail servers, your emails simply disappear into the void. Even worse, incorrect MX records can make your domain vulnerable to email spoofing and phishing attacks.
CNAME Records create aliases for your domains. These are particularly prone to problems because they create dependencies. If the target of your CNAME becomes invalid, your subdomain breaks. This happens frequently with third-party services—you set up a CNAME pointing to a vendor’s platform, then months later they change their infrastructure without warning.
SPF, DKIM, and DMARC Records are essential for email authentication and security. Without proper SPF records, your legitimate emails might be marked as spam. Missing or incorrect DMARC records mean you have no visibility into who’s trying to send emails using your domain name.
TXT Records serve various purposes, from domain verification to security policies. These often get set up once and forgotten, but they need regular verification to ensure they’re still valid and serving their intended purpose.
The Hidden Danger: Forgotten Subdomains
Here’s something that keeps me up at night: subdomain takeover attacks. This happens when you have a subdomain pointing to a service you no longer control. Maybe you set up blog.yourcompany.com pointing to a Tumblr or Medium publication, then cancelled that account. The DNS record remains active, but an attacker can now register that same account name and suddenly they’re hosting content on your subdomain—with your company’s branding and trustworthiness.
I regularly audit the domains I manage and almost always find forgotten subdomains. There’s usually a dev.example.com that some developer created two years ago for testing, or an old campaign subdomain that’s still resolving but pointing to nothing. Each of these is a potential security risk.
What to Check Regularly
Resolution Time and Performance: Slow DNS resolution adds latency to every request. If your nameservers are responding slowly, every visitor experiences delays before your site even begins to load.
TTL Values: Time To Live settings determine how long DNS records are cached. Extremely high TTL values can prevent quick updates when you need them. Very low values create unnecessary load on your nameservers.
Nameserver Availability: You should have multiple nameservers for redundancy. If one fails, the others need to be ready to handle queries. Regular monitoring ensures all your nameservers are responding correctly and serving identical records.
DNSSEC Status: If you’ve implemented DNSSEC for additional security, you need to monitor it continuously. DNSSEC failures can make your entire domain unreachable, and the error messages users see are often confusing and technical.
Common DNS Problems and Their Impact
Stale records pointing to decommissioned servers are probably the most common issue. When you shut down a server or cancel a service, those DNS entries don’t automatically disappear. They sit there, potentially causing errors or—worse—creating security vulnerabilities if someone else acquires that IP address.
Misconfigured propagation timing causes problems during migrations. I’ve seen companies plan careful server migrations, update their DNS records, then panic when half their users still see the old site hours later because they didn’t account for DNS caching.
Missing or incorrect email authentication records result in deliverability problems. Your marketing emails land in spam folders, your transactional emails never arrive, and you have no idea why until someone checks the DNS configuration.
Building an Effective Monitoring Strategy
Manual DNS checks are tedious and error-prone. You need automated monitoring that continuously verifies your DNS health. Set up alerts for any changes to critical records—if someone accidentally modifies your MX records or your A records start resolving differently, you want to know immediately, not when users start complaining.
Implement regular discovery scans to find all subdomains associated with your domain. Many organizations are shocked to discover how many subdomains exist in their DNS that nobody remembers creating. These forgotten corners of your infrastructure often have the weakest security and most outdated configurations.
Monitor from multiple geographic locations. DNS can behave differently depending on where queries originate, especially if you’re using geographic load balancing or CDN services. What works perfectly from your office might fail for users in other regions.
The Bottom Line
DNS health monitoring isn’t glamorous work, but it’s absolutely critical. The problems it prevents—outages, security breaches, email deliverability issues, performance degradation—all have real costs measured in lost revenue, damaged reputation, and wasted time firefighting emergencies. Set up comprehensive monitoring once, and you’ll sleep better knowing that your DNS infrastructure is solid and any problems will be caught before your users notice them.