01 / Domains & DNS
One name. Different connections.
A domain is a name you can build around. DNS provides information that helps clients find the services behind it.
From a name to an answer
A website and an email service can use the same domain while running on different hosts. DNS records describe these destinations. The diagram shows a lookup, not the route taken by website traffic or email.
The lookup returns records.
A / AAAAIP addressesFor hosts such as your web server.
MXMail serversHosts that receive mail for the domain.
TXTText recordsUsed for verification and policies such as SPF.
Read what is published
Open DNS Lookup to inspect the records returned for a domain. Compare the record type and value with the settings your service provider expects. WHOIS is a separate view of registration information; its fields depend on the domain and what the source publishes.
- A and AAAA records contain IP addresses. MX records identify mail servers.
- TXT records carry text used by services for purposes such as verification and email policy.
- A missing result or failed lookup needs context. It does not by itself establish that a domain is available to register.
Troubleshoot one layer at a time
Start with the name and the service that is failing. Inspect its records, then check the service itself. A correct DNS answer alone does not establish that the website or mail server is working.
- Check that you entered the intended domain or host.
- Compare the returned records with the service provider’s documented settings.
- For a website, continue with SSL Checker. For email, continue with the security and email guide.
Who owns the domain? Read our WHOIS guide.