What Is DNS?

The address book for your domain

When someone types your web address into a browser, their computer doesn't know where your website lives. It looks your domain up in a directory called DNS, which hands back the location of the server your site is on. The same thing happens when someone emails you: their email system looks up where mail for your domain should go.

So DNS is the address book that connects your domain name to everything that uses it. You'll mostly never think about it. It matters on the day something changes.

Your domain, website, and email are separate things

This is the part worth remembering. Your domain name, your website, and your email can all live with different companies, and DNS is what ties them together.

That's good news. It means you can move your website to a new host without changing your domain, or switch email providers without touching your website. It also means a change in one place can break something somewhere else if nobody's paying attention. Website, Domain, and Email: Three Different Things covers how to find out who holds each one.

Changes take time to spread

When you point your domain somewhere new, for a new website or new email, the change doesn't reach everyone at once. Computers around the internet remember the old answer for a while before they check again. It's usually a few hours and can take up to a couple of days.

That's why a website move can look finished on your computer while a customer still sees the old site. Plan big changes for a quiet day, not the morning of a launch.

Email depends on it too

Part of your DNS tells the world which company handles your email. If that part points the wrong way, mail to you stops arriving, and nobody gets an error they'd notice.

Another part tells other email systems which servers are allowed to send mail as you. When that's missing or wrong, your messages are more likely to go to spam. SPF, DKIM, and DMARC: Why Your Email Goes to Spam explains that piece.

What to ask before anyone touches it

Whenever a web designer, email provider, or IT person says "I need to update your DNS," ask three questions:

1. What exactly are you changing, and will it affect email or only the website?
2. Can you write down the current settings first, so we can put them back if something breaks?
3. When will it happen, and how will we know it worked?

Those three questions head off the classic "our email stopped working after the website launch" problem.