When you browse the Web, you’ll notice an increasing number of sites and apps asking for a piece of basic information that you probably hand over without hesitation: your e-mail address.

It may seem harmless, but when you enter your e-mail, you are sharing a lot more than just that.

First, it helps to know why companies want e-mail addresses. To advertisers, Web publishers and app makers, your e-mail is important not just for contacting you. It also acts as a digital breadcrumb for companies to link your activity across sites and apps to serve you relevant ads.

If this all sounds familiar, that is because it is.

For decades, the digital advertising industry relied on invisible trackers planted inside websites and apps to follow our activities and then serve us targeted ads. There have been sweeping changes to this system in the past few years, including Apple’s release of a software feature in 2021 allowing iPhone users to block apps from tracking them and Google’s decision to prevent websites from using cookies, which follow people’s activities across sites, in its Chrome browser by 2024.

Advertisers, Web publishers and app makers now try to track people through other means – and one simple method is by asking for an e-mail address.

Imagine if an employee of a brick-and-mortar store asked for your name before you entered. An e-mail address can be even more revealing, though, because it can be linked to other data, including where you went to school, the make and model of the car you drive, and your ethnicity.

“I can take your e-mail address and find data you may not have even realised you have given to a brand,” said Mr Michael Priem, chief executive of Modern Impact, an advertising firm in Minneapolis. “The amount of data that is out there on us as consumers is literally shocking.”

Advertising tech is continuing to evolve, so it helps to understand what exactly you are sharing when you enter an e-mail address. From there, you can decide what to do.

For many years, the digital ad industry has compiled a profile on you based on the sites you visit on the Web. Information about you used to be collected in covert ways, including the aforementioned cookies and invisible trackers planted inside apps. Now that more companies are blocking the use of those methods, new ad targeting techniques have emerged.

One technology that is gaining traction is an advertising framework called Unified ID 2.0, or UID 2.0, which was developed by The Trade Desk, an ad technology company in Ventura, California.

Say, for example, you are shopping on a sneaker website using UID 2.0 when a prompt pops up and asks you to share your e-mail address and agree to receive relevant advertising. Once you enter your e-mail, UID 2.0 transforms it into a token composed of a string of digits and characters. That token travels with your e-mail address when you use it to log in to a sports streaming app on your TV that uses UID 2.0. Advertisers can link the two accounts together based on the token, and they can target you with sneaker ads on the sports streaming app because they know you visited the sneaker website.

Since your e-mail address is not revealed to the advertiser, UID 2.0 may be seen as a step-up for consumers from traditional cookie-based tracking, which gives advertisers access to your detailed browsing history and personal information.

“Websites and apps are increasingly asking for e-mail authentication in part because there needs to be a better way for publishers to monetise their content that is more privacy-centric than cookies,” Mr Ian Colley, chief marketing officer of The Trade Desk, said in an e-mail. “The Internet is not free, after all.”

However, in an analysis, Mozilla, the non-profit that makes the Firefox Web browser, called UID 2.0 a “regression in privacy” because it enables the type of tracking behaviour that modern Web browsers are designed to prevent.

There are simpler ways for websites and apps to track your Web activity through your e-mail address. An e-mail could contain your first and last name, and assuming you have used it for some time, data brokers have already compiled a comprehensive profile on your interests based on your browsing activity. A website or an app can upload your e-mail address into an ad broker’s database to match your identity with a profile containing enough insights to serve you targeted ads.

The bottom line is that if you are wondering why you are continuing to see relevant ads despite the rise of privacy tools that combat digital tracking, it is largely because you are still sharing your e-mail address with various websites, allowing you to be tracked.

So, what to do?

1. Create a bunch of e-mail addresses

Each time a site or an app asks for your e-mail, you could create a unique address to log in to it, such as, for example, netflixbrianchen@gmail.com for movie-related apps and services. That would make it hard for ad tech companies to compile a profile based on your e-mail handle. And if you receive spam mail to a specific account, that will tell you which company is sharing your data with marketers. This is an extreme approach, because it is time-consuming to manage so many e-mail addresses and their passwords.

2. Use e-mail-masking tools

Apple and Mozilla offer tools that automatically create e-mail aliases for logging in to an app or a site; e-mails sent to the aliases are forwarded to your real e-mail address. Apple’s Hide My Email tool, which is part of its iCloud+ subscription service that costs 99 US cents (S$1.30) a month, will create aliases, but using it will make it more difficult to log in to the accounts from a non-Apple device. Mozilla’s Firefox Relay will generate five e-mail aliases at no cost; beyond that, the program charges 99 US cents a month for additional aliases.

3. When possible, opt out

For sites using the UID 2.0 framework for ad targeting, you can opt out by entering your e-mail address at https://transparentadvertising.org (Not all sites that collect your e-mail address are using UID 2.0, however.)

You could also do nothing. If you enjoy receiving relevant advertising and have no privacy concerns, you can accept that sharing some information about yourself is part of the transaction for receiving content on the Internet.
NYTIMES