Privacy
Everything else hangs off it
An account's email links uploads, results and payments across time, and a reused address links them to everything else that address touched.
Guides on Privacy: Who could see it, how, and what each path costs to close, Soft delete, backups, caches and logs, Sometimes, and the policy clause that says so is easy to miss
Of every identifier a rating site collects, the email address does the most work. It is stable, self-reported, and usually the single field a database uses to join an account to every upload and result it has ever produced.
An IP address rotates, a device fingerprint drifts as browsers update, a card number sits with the processor rather than the site.
Why it outlasts the other signals
IP addresses and device fingerprints identify a session or a machine, and both change: a new router, a new phone, a cleared browser profile, and the trail breaks. An email address does not change unless you decide to change it, which almost nobody does, because the cost of updating every service that has it is high enough that people tolerate the alternative. That persistence is exactly what makes it the field worth protecting first if anonymity matters to you. Data protection law treats it accordingly: the UK Information Commissioner's Office guidance notes that "a name and a corporate email address clearly relates to a particular individual and is therefore personal data."
The reuse problem
The address itself carries more history than the site ever sees directly. If you have used the same email anywhere else - a forum, a dating profile, a work account, a breached service from years ago - a data broker or a simple reverse search can connect that address to a real name, because somewhere in its history it was typed into a form that asked for one. A payment made with the same account closes that loop completely, since the processor's billing name and the account's email now sit on the same transaction record.
What actually helps
A dedicated address, created for this purpose alone and never reused elsewhere, breaks the reuse chain without breaking the site's own functionality. An alias service that forwards to a real inbox while showing the site a disposable address does the same thing with less setup, at the cost of trusting the alias provider instead. Neither removes the account-to-upload link inside the site's own database, which is a separate question the site's retention policy answers, but both stop that link from reaching further than the site itself.
Rate Cock requires an email to create an account, which is standard for a tool that needs to return results and manage a history, and a dedicated address used only there is the cheapest way to keep that requirement from becoming a wider identifier. The same reasoning applies wherever an account exists at all; Penis Rater's guide to evaluating a scoring tool touches on account requirements as one of the things worth checking before signing up anywhere. Method-based tools ask for the same field to send a report; Measure My Cock's data page covers what an account email is used for once a measurement is on file. A commissioned human review sidesteps the reuse question in a different way, since the arrangement is named to the reviewer from the start; Rate Penis covers how that process handles contact details.