DNS (Domain Name System).

Computers find each other on the internet by IP address; people use names. DNS connects the two. When someone types an address into the browser, the device asks a DNS resolver, usually run by the internet provider or by services such as Cloudflare or Google. The resolver works its way down the hierarchy: from the root servers to the servers of the top-level domain (for .ch that is the registry SWITCH) and on to the name servers responsible for the specific domain. That is where the records live that say where the request should go.

For an ordinary SME website only a handful of record types matter. An A record points to an IPv4 address, an AAAA record to an IPv6 address. A CNAME record points one name to another, for instance www.example.ch to the hosting provider. MX records determine the mail server. TXT records hold text used for verification — for SPF, DKIM and DMARC, for example, or for confirming the domain in Google Search Console.

Every record carries a TTL (Time to Live), which sets how long resolvers may cache the answer. A TTL of 3,600 seconds means that after a change it can take up to an hour before every visitor sees the new address. Before a planned migration you therefore lower the TTL to a few minutes several days in advance — the switch-over then goes through almost immediately.

Many website and email problems are really DNS problems: a site that only loads with www after a relaunch, mail that stops arriving after a change of hosting provider, or newsletters that land in spam. The cause is almost always a missing, duplicated or incorrect record. Whoever holds access to DNS management effectively controls the entire online presence — which is why that access belongs inside the company, not just with the agency.