Also 3.3 billion unique emails are strictly more interesting than just the addresses since an email includes adresseses and a subject line by definition.

Obviously, if you have emails that were generated in different events, thus having different Message-ID and timestamp fields, they will be unique.

But non-uniqueness could crop up in a dataset for various reasons. As the simplest example, imagine this guy aggregated datasets A, B, and C, but it turns out C was itself already an aggregate of A and B. Then all the emails in A and B would be duplicated in the final dataset.

So of course when publishing some huge collection of data from many different sources, it's useful to make sure each piece of data is unique, and the title is just pointing out that for this data set, that has indeed been done. This logic applies whether the data is messages or addresses.

If you just look at the body text, and not the headers, it is even less likely for emails to be unique due to mass spam.

> Mentioning that the email addresses are unique is making the point that we've identified just as many people, which is interesting.

No it isn't. He didn't say that the addresses correspond to unique _people_, just that they are unique addresses, textually. The mapping of email addresses to people is not even close to one-to-one.

> Also, people are usually more concerned with the information in the email rather than the count. Most/a lot of the value of an email comes from the information in it.

But the article/headline isn't just saying a count was published, it's saying the emails themselves were leaked. If this meant email messages rather than addresses, then it would indeed mean the valuable information in the emails had been compromised. Why are you saying that wouldn't be interesting?

> If I were to release 3.3 billion emails between random low-profile office workers (let's say) which contain nothing interesting, I'm not so sure that would make a headline.

I think it would, assuming they were between humans and not just spam. A leak of 3.3 billion ostensibly private messages, on any platform (email, twitter DMs, whatever), would be by far the most serious data breach in the history of the internet.