(Confusingly, there were many more versions of Netscape after 4, but Mozilla Suite didn't really derive from them. Netscape 6 and 7 were just contemporary versions of Mozilla Suite with some Netscape badging slapped on. Netscape 8 was based on early versions of Firefox, dropped the other non-browser "suite" components, and was only released for Windows. Netscape 9 was also a browser-only thing, but went back to being cross-platform.)
I think it would be just slightly more accurate to say, that it didn't derive from them at all, as the original Netscape codebase was scrapped.
https://en.wikipedia.org/wiki/History_of_Mozilla_Application...
[1] There's a few more directories that are split out of mailnews, due more to historical reasons than any sane code split.
Seamonkey
Netscape Mail -<
Thunderbird