Upvote:3
Ok, this is the authoritative answer i was looking for:
Foreigners awaiting renewal of their residence permits can leave
and re-enter Italy if they hold:
1. the receipt issued by Italian Post offices (Poste Italiane S.p.A) certifying the submission of the application for renewal of their residence permit or EC residence permit for long-term residents;
2. the expired residence permit;
3. their passport or other equivalent travel document .
source is here
This applies to those waiting for the document for the first time:
The same facilitated procedure is granted to foreigners who have submitted their
application for their first residence permits for employment,
self-employment, or family reunification, provided that:
1. they leave and re-enter Italy through any Italian external border crossing point (cicular letter 11th March 2009);
2. they show their passport or other equivalent travel document, along with the entry visa specifying the reasons of their stay (employment, self-employment, or family reunification ) and the receipt issued by Italian Post offices (Poste Italiane S.p.A.);
3. they do not transit through other Schengen countries, as this is not allowed.