First the good news: Platinum 4.2 has the Newsletter system professional version integrated. There is no more the basic version so all can have statistics panel and bounce management after the upgrade.
Newsletter configuration is now part of the platinum.conf and the old newsletter.conf is deprecated. This choice was driven by the new contextualized platinum.conf that lets to have only one Platinun package which adapts it self to the deployment environment.
Every configuration keys about Newsletter system is prefixed with "newsletter." and rich samples of configuration can be found inside the platinum-sample.conf.
So the first step to migrate from 4.1 to 4.2 is to remove the newsletter.conf and move the configurations inside the platinum.conf. Pay attention that even the syntax has been changed!
The bounce management
Now each installation must have its own bounce mailbox, so the internal problems to have a unique installation identifier has been removed. See the article Newsletter and Bounces.
It's a googd practive to have separated mailboxes for each Platinum because it's easy to maintain them (manully) when needed and it's a reat performance boost while Platinum checks for bounced addresses.
The old Newsletter Pro application
On installations using the "Newsletter Pro" application (folder admin/apps/newsletterPro), that folder can be safely deleted since the pro features has been added to the standard Newsletter application (folder admin/apps/newsletterPro).