What Are Subdomains? A Simple Guide to Using app, blog, and More

How Subdomains Work

Think of your main domain (yourcompany.com) as your company’s office building. When someone visits that address, they arrive at your main entrance – your marketing site. But what if you have a separate web app, a blog, or a help center? You can’t move the whole building, so you create dedicated entrances for those services: app.yourcompany.com, blog.yourcompany.com, docs.yourcompany.com. Those are subdomains. A subdomain is simply a prefix added to your main domain name. It creates a separate web address that can point to a completely different place – a different server, a separate hosting provider, or even a third‑party service like Shopify or WordPress. The “layers” idea comes from the fact that each subdomain can live on its own and be managed independently, just like different floors or departments in a building. Even though they share your main domain name, subdomains are treated by the internet as distinct destinations. That means you can give one team control of docs.yourcompany.com without touching your main marketing site, and you can point app.yourcompany.com to a cloud platform while blog.yourcompany.com sits on a separate blogging service.

Real-World Analogy

Imagine your domain as a phone system. The main number (yourcompany.com) connects callers to your reception desk. Subdomains are like extension numbers: dial extension 101 for the app department, extension 102 for the blog, extension 103 for documentation. Instead of dialling a number, people type a prefix before your domain, and DNS instantly routes them to the right department’s server.

When someone types blog.yourcompany.com into their browser, here’s what happens in plain terms: the browser asks the internet’s address book (the Domain Name System, or DNS) “Where is blog.yourcompany.com?” DNS checks the records you set up for that subdomain and replies with an IP address or the name of another server. The browser then travels to that location and loads the blog. From the visitor’s point of view, it’s just a website, but behind the scenes your subdomain pointed them to a completely different destination than your main site.

That’s the big idea: a subdomain gives you a separate signpost that can point to anything you want. The setup lives in your domain’s DNS settings, and you can change the destination any time without touching your main website.

Technical Details

▸ → A record to IP 203.0.113.5 (your main web server)

▸ → CNAME record pointing to hosting.herokuapp.com (your application platform)

▸ → CNAME record pointing to blogs.examplebloghost.com (a managed blogging service)

▸ → A record to 192.0.2.60 (a separate documentation server)

▸If a subdomain sends email (like marketing emails), it needs its own SPF and DKIM records in DNS. Most subdomains used for websites don’t need these.

▸Subdomain records are independent – you can delete one without affecting the others.

Why It Matters for Your Business

When you use subdomains intentionally, you get a clean, secure structure. Marketing runs the main domain and blog; product owns the app and docs; security can isolate API endpoints. No one team steps on another’s toes, and each service can be hosted on the platform that works best for it.

Misconfigured subdomains, on the other hand, can quietly damage your credibility. A forgotten blog subdomain that shows an error page tells visitors you’re not paying attention. Worse, if you point a subdomain to a third‑party service you later cancel (like a temporary campaign site), an attacker could potentially re‑register that service and take over the subdomain. Your customers would see a malicious page that uses your company’s exact domain name.

This matters for anyone who relies on your brand online – marketing, sales, customer support, and especially your leadership team. A subdomain isn’t just a tech detail; it’s part of your public face. Knowing what subdomains exist and keeping them healthy protects your reputation and stops embarrassing (or dangerous) surprises.

Common Issues and Warning Signs

Problems with subdomains usually fall into two buckets: you’ve lost track of them, or they’re pointing to something that no longer exists. Here are the red flags to watch for:

Common Issues

You visit a subdomain your team used to use (like ) and get a “server not found” error or a blank page – the DNS record might be missing, or the target service is gone.

You discover a subdomain you never knew existed, like – someone may have created it long ago and never documented it.

Your domain scan (like a TechSpy report) warns about “subdomain takeover” risks – typically because a CNAME record points to a cloud service you no longer use.

A subdomain you set up for a one‑time campaign still resolves years later, displaying outdated content – it’s a liability and a potential phishing magnet.

An important business function (like ) is down because its DNS record was accidentally changed – and nobody noticed the connection.

How to Fix or Improve Subdomains

Getting control of your subdomains starts with a simple audit. Even if you don’t manage DNS yourself, you can take the first step and hand the rest to your IT person.

Once you’ve tidied up, run a TechSpy scan on your domain. It will automatically detect subdomains and flag any that still pose a takeover risk – giving you peace of mind that every corner of your domain is in shape.

1Make a list of every subdomain you know about. If you have access to your DNS control panel (usually your domain registrar or hosting provider), browse the records and write down everything that appears as a separate hostname – e.g., , , , . If you don’t manage DNS, ask your IT team or agency to provide this list.

2Verify each subdomain’s target. For A records, note the IP address. For CNAMEs, note the exact destination (like ). Make sure that destination is a service you actively use and control. If you see something pointing to a service you cancelled or never heard of, flag it.

3Delete subdomains you no longer need. If you’re certain nothing important depends on a subdomain, remove its DNS record. This prevents the risk of someone hijacking a dead pointer. Only do this if you’re certain – if in doubt, ask a colleague.

4For new subdomains, choose the right record type. If you’re pointing to your own server with a fixed IP, use an A record. If you’re using a platform like Shopify, Webflow, or a hosted blog, they’ll almost always give you a CNAME destination. Add the record in your DNS panel and wait a few minutes for it to propagate.

5If you don’t manage DNS, forward this checklist. Share it with your IT person or agency, and ask them to run through it for every subdomain your company uses.