This raises an interesting question: should email addresses be private?
GDPR is clear on this and there have been significant fines for revealing email addresses against the will of their owners (e.g. using cc instead of bcc). Not saying this is the ultimate wisdom, just a data point to consider.
By itself or linked to other data?
Afaik PII is usually a set of linked data. As in common name and surname are not PII. Together with age, they can be.
