[trampypizza]

Yes, you are correct. I think it would be extremely difficult to justify that this kind of processing was necessary for the provision of service.

It seems to me that an organisation the size of Dropbox would have a fairly watertight justification. However if the legal basis for processing is neither consent nor provision of service, then they must have done a pretty good job of obfuscating all PII (as the article says "...we and Dropbox employees could view no personally identifiable information.". If this is the case then this sharing of information may not even be in-scope of GDPR.

I'm not sure if the public interest exceptions would be a safe route to go down. The EU has made it clear that, like 'Legitimate Interest', the get-out-of-jail-free justification is going to be highly scrutinised.

EDIT: I have just seen that the article has been edited to say that the anonymisation and aggregation was carried out by Dropbox before being transferred to the third party, which kind of kills the discussion.