The BambooHR theory is interesting. I looked up email addresses of co-workers at a startup I worked for a few years ago (Jul'15-Jun'16). I was with them earlier in 2012-13. My work email isn't there. But the slice of people between Apr'13-Jul'15...all there.
I guess we ran through a bunch of HR software during the period, BambooHR being one of them. So either it's a subset of BambooHR or its some other product a bunch of people at my workplace signed up for.
Our company's been on BambooHR for 3-4 years now I think (me personally for a little over two). Can't find any of our company's addresses in there. So either partial or old if that's where it came from.
Others are saying they've found data from as recently as mid-2019, so could be possible that the reason it's so hard to find a source is that this is multiple sources. Looking at this as a dump from some sort of contact manager, could see this being a dump from some sales guy's CRM or something where he'd imported multiple datasets as potential leads alongside his personal contacts.
