Here is your formula in an easier form (at leat for me) It is basically asking to evaluate if the ClubMember.email is are not one of...
not({ClubMember.email} in ["x@y.co.uk", "z@n.com", "g@.co.uk","n@l.co.uk"])
or for you suppression - suppress is email is one of these
{ClubMember.email} in ["x@y.co.uk", "z@n.com", "g@.co.uk","n@l.co.uk"]
Mike