RHL 9.0 and older releases shipped Postfix 1.x. severn includes Postfix 2.0. Besides adding many new features, Postfix 2.0 will require some reconfiguration by users upgrading from 1.x to 2.0, and should be mentioned in the release notes. In addition, RHL 9.0 and older releases shipped Postfix chrooted. Users upgrading from old releases to Postfix 2.0 will still have a chrooted Postfix. Users doing a new install of Postfix 2.0 on severn will get a non-chrooted Postfix. This needs to be mentioned as well, since configuration of some aspects of Postfix is very different when chrooted and when not chrooted.....
Good point -- it'll be mentioned in the next iteration of the release notes...