PrintGet the app

Privacy Policy

Last updated: August 31, 2026

Sudoku a Day is operated by Ocho B.V. This policy explains what we collect, why we use it, and the choices you have. We do not sell personal data.

What we collect

  • Game and account data: puzzle progress, scores, leaderboard entries, profile details you choose to provide, and the technical identifiers needed to keep that data synchronized.
  • Basic usage data: limited technical and aggregate usage information used to keep the site reliable and understand general product use.
  • Optional Sudoku emails: your email address, daily or weekly schedule, IANA time zone, local delivery hour, difficulty, paper size, consent version, confirmation and unsubscribe history, and delivery outcomes such as a bounce or spam complaint.
  • Abuse prevention: short-lived, one-way identifiers derived from an email address or IP address for rate limiting. We do not store the full IP address in the subscriber database.

How we use the data

  • Provide the puzzle, profile, score, and leaderboard features you use.
  • Generate and deliver the Sudoku schedule you explicitly confirmed.
  • Remember and apply email preferences and unsubscribe requests.
  • Prevent duplicate mail, abuse, hard-bounce retries, and mail after a complaint.
  • Secure, debug, and improve the service.

Recurring Sudoku email is based on your consent. Downloading a PDF does not require consent to email, and an address is not activated until its owner confirms the request. You can withdraw consent at any time using the prominent unsubscribe link in every recurring email.

Services that process data for us

Cloudflare hosts the website, subscriber database, generated PDFs, queues, bot protection, and scheduled jobs. Amazon Web Services Simple Email Service delivers email and reports delivery, bounce, and complaint events. Other service providers used by the game may process only the data needed to provide their part of the service. We remain responsible for how the data is used and do not permit providers to use subscriber addresses for their own marketing.

Email tracking

Sudoku emails do not contain advertising trackers. We do not enable open or click tracking. We record operational delivery events needed to know whether a message was delivered, bounced, rejected, or reported as spam.

Retention

  • Unconfirmed email requests are removed after seven days.
  • Rate-limit records are removed after they expire, normally within 24 hours.
  • Raw email-provider event details are removed after 30 days.
  • Routine operational delivery records are removed after 90 days.
  • Consent evidence is kept while a subscription is active and for a limited period afterward when needed to demonstrate that mail was requested.
  • A minimal unsubscribe, hard-bounce, or complaint suppression may be kept so that we do not accidentally start sending again.

Your choices and rights

Every recurring email lets you change the schedule or stop all Sudoku emails without an account, password, survey, or hidden extra step. You may also ask us to access, correct, export, or delete personal data where applicable. A suppression needed to honor an unsubscribe or complaint may be retained in minimal form.

Contact

For privacy questions or requests, email hi@ocho.so.