This is an informative summary of the information that hotels and other accommodation providers in Spain are required to collect from guests: https://www.minut.com/es/blog/registro-de-huespedes-automatizado-guia-practica-2025
Email addresses, along with mobile phone numbers, are among the pieces of information that hotels are legally required to collect. If they don’t, they could face fines of up to 30,000 euros. If a guest refuses to provide this required data, the hotel is allowed to cancel the reservation and end the service agreement.
This information is sent to Spain’s Ministry of the Interior through the official SES.HOSPEDAJES system. This platform is subject to the full legal protections of the European Union’s GDPR (Regulation EU 2016/679), which governs the handling of personal data. For our American friends who might be uneasy about handing over personal details, GDPR protections are significantly stronger than anything currently offered in the United States—much stronger than laws like the California CCPA or CPRA. There’s a proposed federal law in the U.S. called the ADPPA (American Data Privacy and Protection Act), which would bring the country closer to the GDPR standard, but it’s still under debate and hasn’t been passed yet.
Personal comment: One could reasonably question the requirement to provide an email or even a mobile number, since these are not things people are universally expected to have. Unlike an address (everyone lives somewhere), a passport (required for international travel), or a date of birth (which everyone has), not everyone needs to have a mobile phone or an email account. In fact, there have been formal objections on this point presented in the Spanish Parliament. But so far, the officials at Spain’s Ministry of the Interior—an institution still influenced by the authoritarian mindset inherited from the dictatorship era—have decided that we must all have both an email and a mobile phone number.
So, my advice: just create a new email address for yourself and get done with it, even if you never plan to use it again.