I'm a native Spaniard as well. Do you write emails with opening marks?

Perhaps it's a generational thing, but so far I've worked for two multinationals including a bank and I can't think of a single person that bothered to do so, except for official communications that are usually edited by someone whose very job is to do that.

Neither did my teachers at University, and frankly I wouldn't be surprised if the official rules are changed in the next couple of decades.

A different Spaniard here: I do write opening marks everywhere including emails, and I would expect that to be a generational thing as you suggest. I’m sad but not surprised to see those parts of the language being lost for many/most people.