@davidesimoncini - I think that you can mention up to 10 people, any more than that and they won't receive a notification. The exception being if you have a low reputation - if your reputation is low (e.g. a new user), then their notifications aren't received either.

So most mentions will receive a notification. If I were to use say @davidesimoncini, @davidesimoncini, @davidesimoncini - that would count as 3 of your 10 mentions so when tagging somebody, try to avoid multiple mentions.