[dragonwriter]

> In this context, I am wondering about its usage w.r.t. the email to buzzfeed, is that considered "publishing".

Publishing for purpose of defamation is communicating the message to another person by any means.

> If not, I would have thought then that the libel would be on buzzfeed side, for publishing unsubstantiated rumors

BuzzFeed published true facts, to wit, that Elon Musk had mailed them certain claims. Falsity being a required element of defamation (whether libel or slander), their publication can not be defamatory.

> if they had caveat with "Musk emailed this to us..." .

That's not a caveat, it indicates a completely different fact claim; the claim “Joe said X did Y” is a distinct fact claim from the claim “X did Y”.

[buchanan]

> Publishing for purpose of defamation is communicating the message to another person by any means.

So, even if buzzfeed had not published to their website, Musk had already published to buzzfeed. Interesting !