How DNS works: a UK small business guide

Someone tells you to add a TXT record to verify your domain, or change an MX record so a new email provider works. You open the DNS settings, see a wall of acronyms, and quietly close the tab again. That hesitation is completely normal, and it costs businesses real time and money.

The reassuring truth is that DNS is built on one simple idea. Once that idea clicks, the acronyms stop being intimidating and start being useful.

The internet address book#

Computers do not find each other by name. They find each other by number, an IP address that looks something like 203.0.113.10. People, on the other hand, are good at names and hopeless at remembering numbers. DNS, the Domain Name System, is the address book that translates the one into the other.

When someone types your domain into a browser, their computer asks the DNS system where that name actually lives, gets back an address, and connects. All of this happens in a fraction of a second, every single time, for every visitor. If you want the gentle version of what a domain name even is, the MDN explainer on domain names is a friendly place to start. The whole structure is coordinated globally by IANA, which oversees the root of the system that everything else hangs from.

The records that matter#

Your domain's DNS settings are a small list of records, each doing one job. You will rarely touch most of them, but it helps to know what the common ones are for.

A and AAAA#

An A record points your domain at an IPv4 address, the classic numbered address. An AAAA record does the same job for the newer IPv6 format. In practice these are what send visitors to the server that holds your website. Change the A record and you change where your site lives.

CNAME#

A CNAME record is an alias. Instead of pointing at a number, it points at another name. This is how a subdomain like shop.yourbusiness.co.uk can be made to follow wherever the main name goes, which saves you updating several records every time something moves.

MX#

MX records handle email. They tell the world which servers should receive mail for your domain. Get these wrong and your website can be perfectly fine while every email silently fails. If you ever switch email provider, the MX records are almost always the thing you need to change.

TXT#

TXT records hold short pieces of text that other systems read. They are used to verify that you own a domain and, importantly, to publish the email authentication records that stop your messages being marked as spam. The detail of how DNS stores all of this is defined in RFC 1035, the long standing specification the whole system follows.

TTL and why changes take time#

Here is the part that catches people out. You change a record, refresh your site, and nothing happens. You assume you got it wrong. Often you did not. You are simply waiting for TTL.

TTL, or time to live, is a number attached to each record that tells the rest of the internet how long it may cache the old answer before checking again. Set to an hour, that old answer can linger for up to an hour around the world even after you have changed it. This caching is what keeps DNS fast, but it is also why changes are never instant. A clear explanation of the moving parts lives in the MDN glossary entry for DNS if you want the slightly deeper version.

The practical tip is to lower the TTL on a record a day before you plan to change it. Drop it to a few minutes, make your change, and the rest of the world picks it up quickly rather than clinging to the old value all afternoon. The concepts and facilities behind this caching are laid out in RFC 1034 for anyone curious about why it works the way it does.

Common mistakes that break email#

Most DNS disasters are not exotic. They are small slips with big consequences, and email suffers more than anything else.

The classic mistake is changing your website host and accidentally wiping the MX records in the process, so the site loads but the mail vanishes. Another is forgetting to copy across the TXT records that authenticate your email, after which your perfectly legitimate messages start landing in junk. A third is a stray typo in a record, a missing full stop or an extra space, that quietly breaks one service while everything else looks fine.

None of these are hard to avoid. Before you change anything, write down what the current records are, so you can put them back. Treat the MX and TXT records with particular care, because they are the ones that affect mail.

Getting help with your zone#

You do not have to manage all of this alone, and you certainly do not have to learn it under pressure during a migration. If editing records by hand makes you nervous, our DNS management tools give you a clear interface rather than a raw text file, and support can make the trickier changes with you.

If you are still choosing or moving a name, our domains section covers registration and transfers in plain terms. The underlying protocols, including how queries travel and how DNSSEC adds a layer of trust, are all public and documented through bodies like the IETF, so nothing about DNS is secret. It only looks that way from the outside.

Learn the handful of records above and the next time someone asks you to add a TXT record, you will know exactly what they mean, why it matters, and roughly how long it will take to work.