I was browsing around and Seamonkey still exists, still releasing new versions? So cool. This is a continuation of the Mozilla Suite and Netscape Communicator before that, back when it was more common to have a software collection with web browser, email & news, html composer all in one.
Hnnngggg that old interface, those cute buttons and small panel grabbers 
https://www.seamonkey-project.org/
@workingclassgames And full themes! So besides the included Modern there are also more themes out there. Unmaintained ones may need adjustments, though.
(And it also has an IRC client and Lightning for calendar stuff in Mail&News; Gopher support can be re-added with OverbiteFF (with one modification?). And the web browser can also load news: URLs)