Um, not if the user signed up for it? Believe it or not lots of people sign up for email lists — especially editorial ones but also commercial ones — on purpose. Not just normies either, I bet there are plenty of people on HN who've subscribed to a bunch of bloggers' lists. I certainly have.
Thank you for the comment. The site already has RSS, and I'd agree there are good technical grounds for preferring it, but I get the impression that its use among users is declining, which is why I was considering other mechanisms. I find it an interesting point of view to consider a feature which alternatively allows users to opt-in to email notifications - but which doesn't disadvantage them at all if they don't - as "user-hostile". (But of course I've seen sites which want to coerce visitors to hand over an email address to be able to access the content they were expecting, and depending on context, I can see cases where that could be considered aggressive.)