Data onboarding is the process of matching a brand's own customer list, kept in its own systems, to those people's identities online, so that the brand can reach them with advertisements. Neither the brand nor the advertising platform sees the other's data. The service is sold mainly in the United States, where it began as a business in its own right.
The word "offline" matters here. Many customers are known to a brand only from offline records: the billing counter of a store, a warranty card or a call centre. These records hold an email address, a phone number or a postal address. But online advertising does not use names. It uses device identifiers, browser cookies and connected-TV identifiers. Data onboarding connects the two.
The process has a few steps. First, the brand converts each email address and postal address into a hash, a scrambled code made by a one-way formula. Next, the onboarding company matches the hashes against its identity graph. Then it replaces each matched person with anonymous online identifiers. The brand never learns which websites a customer visits. The advertising platform never learns the customer's name. The share of the list that is matched is called the match rate.
Say a chain of hardware stores in the United States has 800,000 customers who gave an email or postal address at its billing counters. Before a spring sale, it wants to show a TV advertisement only to them. It hashes the 800,000 records and sends them to the onboarding company. The company matches 520,000 of them, a match rate of 65%. It turns each match into device and TV identifiers, and sends these to a connected TV (CTV) advertising platform. The platform shows the spring sale advertisement to those homes, on streaming apps. Four weeks later, the chain compares the store purchases of the 520,000 with a similar group that did not see the advertisement. This shows whether the advertisement brought people into the stores. Joining store sales back to advertising in this way is called closed-loop measurement.
Brands also use onboarding for the opposite purpose: to remove existing customers from advertisements meant for new ones, so that they do not pay to reach people who already buy. Retailers use it to sell advertising to brands on a retail media network.
For years, onboarding mapped customers to third-party cookies. Today, Safari blocks all third-party cookies by default. Firefox blocks the cookies of known tracking companies by default. It also keeps every other third-party cookie separate for each website, so the cookie cannot follow a person to other sites. Chrome, the most used browser, still allows third-party cookies, because Google decided in April 2025 to keep them. Because Safari and Firefox restrict these cookies, onboarding now maps customers more often to logins and platform identifiers. Privacy rules have also tightened. So many brands now prefer a data clean room, where two companies match their lists without either side receiving the other's records.