When you enrol in Flying Blue, you are required to accept the Flying Blue Terms and Conditions as part of the sign-up process.
This includes the following, under the heading "Enrolment":
1.3.3 When joining the programme, the Member accepts to receive the FB Communication which is a basic part of the programme. The Member is responsible for providing the Company with a correct mailing and emailing address for obtaining his Card and for FB Communication. If a Member changes his mailing/email address, the Member shall notify the Company in writing or by means of the Programme’s website without any undue delay. This change of address should carry the Member’s signature or PIN, whichever is applicable.
1.3.4 Any eligible person wishing to join the Programme must complete and sign up an individual Programme membership application, which the legal guardian or representative must sign if the applicant is a minor. All persons applying for membership of the Programme shall be deemed to have read and accepted the General Terms and Conditions.
As such, all members - including yourself - agree to receive these communications by email by ticking the box.