In the end, I solved the problem of the unwanted e-mails.
I needed to set all the preferences to "no email", except from Individually selected, for which I chose "instantly"; but this didn’t was enough.
As written by oweng I also had to turn, indeed, the Choose email tag filter line to "Exclude ignored tags". I don’t know why, but this is also indispensable for not to receive e-mail updates of ALL the new questions, answers and comments published here. This was, at least, my instance.
It’s not clear why; maybe it’s a bug, as suggested by ROSt52.
Anyway, in these days I haven’t received unwanted e-mails from AskLibO anymore.
Now, I only have to verify that I receive actually the updates of the questions I am following, like this one itself. I will notify if all is running properly.
(UPDATE): Yes, all is working properly.