Everybody can get access to your registration details such as your name, email address, phone, physical address, etc… Those details are publicly available.
If you prefer to hide your details to the public, please choose ID Protect addon for a small extra fee when you register your domain name, on the allowed domain name extensions. Not all the domain extensions allow you to hide your details, such as the .ES for example. General domain names like .COM, .NET etc… allow you to hide your details with ID Protect feature.
ID Protect also helps you by avoiding automatic data collectors to include your email address in spam lists (because your email is hidden and we place an anti spam filter on the email that we publish in the WHOIS data), so you should receive less spam too.