The question is what you do with the e-mail address. e.g., if the page would say:
1. "we provide this book for free, but collect your e-mail to follow up once in about 1 month time with a relevant offer." ==> this might even work from a "legitimate interest" view, but thats currently not well defined
OR
2. "click here to provide consent for us collecting your email and using it for ..., ..., ..."
1. "we provide this book for free, but collect your e-mail to follow up once in about 1 month time with a relevant offer." ==> this might even work from a "legitimate interest" view, but thats currently not well defined
OR
2. "click here to provide consent for us collecting your email and using it for ..., ..., ..."