I requested the job notification some weeks ago and it worked. Last Sunday, I've changed my e-mail settings and since then I haven't been able to receive job notifications anymore.
What exactly did you change? Can you get other notifications (KudoZ or forum)?
I also would like to have a confirmation from yous: is it true that I'm not going to receive a notification for those jobs whose offered rate is lower than my minimum rate (entered here at Proz)?
Correct - however, there's no difference between Platinum and other members as far as this function is concerned.
If so, is there any mean to be informed (by job notification) of this kind of jobs too?
I'm afraid not - and that's by design.
I mean... if I entered that my minimum rate for EN>IT translations is 0.07, and I'm going through a very "calm" period (!) and I'd like to bid for a 0.065 job, how can I be immediately alerted? Apart from going to the "Browse job" page, obviously!
That would be the only way, however, in this case you would not be able to quote at 0.065 - see Rates FAQ #3 for details.