What DNS is, and why your business depends on it.

Computers find each other by number. People remember names. The Domain Name System (DNS) is the directory that connects the two. When someone types your address or sends you an email, their device asks DNS where to go, and the answer comes from records that you control.

Three things people mix up

• The registrar is where the domain name is registered and renewed.
• The DNS host holds the records. It is often the registrar, but it does not have to be.
• The web and email hosts are where the records point.

They can be three different companies with three different logins. Knowing which is which, and who holds each login, is most of the work.

The records you will meet

• A and AAAA point a name at the numeric address of a server.
• CNAME points a name at another name. It is often used for www, or for a service hosted somewhere else.
• MX says which servers receive email for the domain.
• TXT holds text for other systems to read. Email authentication and proof of ownership both use it.
• NS says which DNS host is in charge of the domain.

Why changes are not instant

Every record carries a time to live (TTL), in seconds. It tells other servers how long they may remember the answer before they ask again. If the TTL is one day, a change can take up to a day to reach everyone.

Before a planned move, lower the TTL a day or two ahead. On the day, the change spreads in minutes, and it can be reversed just as fast.

Changing records safely

1. Export or screenshot the current records before touching anything.
2. Change one thing at a time.
3. Check the result from outside the office with a DNS lookup tool.
4. When moving the website, leave the MX and TXT records alone unless the email is moving too.
5. Raise the TTL again once everything has settled.

Protect the domain account

Whoever controls the registrar account controls the website and the email. Keep the domain in the name of the business, not an employee or a former web designer. Turn on multi-factor authentication, turn on automatic renewal, and make sure the contact address on the account is one that somebody reads.