An email hash can be used to identify an individual and so would very much be in the scope of GDPR, the same as any other number used to identify an individual.

An email hash can be used to identify an individual and so would very much be in the scope of GDPR, the same as any other number used to identify an individual. Curious why you think that would not be the case. It seems to fall squarely into Article 4’s definition of personal data.