Buene sera signore.

It is very easy and clear; uno paese=1 country means just that valid ONLY in THAT country-and you as italiano canNOT buy 1 country IT. ONLY the global pass also offers you chance to leave and return in own country on passdays.

As you will know no trains serve islands and also the rail network in GR is quite limited and does not really serve what the normal tourist wants to go to. In the general site find country info and what there is-fair chance you decide it is not for you. BTW; Your TrenItalia is since a few yrs the owner and manager of what was once named OSE and now Hellenic trains. Decide yourself if that is pro or con.

About that ferry pass; Only valid on 2 boat companies and these have no service to all islands. Again same: first do homework and check if they even go to what you want to visit. There are passes for 4 or 6 trips: that for 6 ALSO can be used for 2 trips from+back to IT, but it is by far NOT free=gratis, nullo costo_you still have to pay for port, fuel, other seasonal taxes and it may well be there is another ferry that is cheaper in the end.

Sorry if this is not quite the answer you hoped for-but it is what it is and avoid disappointment later.

Here is an overview for the greek island pass:

https://www.interrail.eu/content/dam/pdfs/pass-guides/Greek%20Islands%20Pass%20Guide%202022.pdf

The 6-day-pass does cover the trip from Italy (there is no exclusion for Italians mentioned). 

In contrast to what have been told in the previous posting, port taxes and fees are included (see page 3). 

Thanks for the reply.

In fact, in the brochure there is no mention of the use of this kind of pass for Italians in order to reach Greek Islands, as there is underlined that the pass is about "days of travel". Unfortunately on the Internet there are a number of "pages" telling trips instead of days and restrictions on the use... 

BTW, now I am much less concerned... 

Thanks again.