That’s my take too, although my personal professional IT experiences are a mere rounding error on yours.
A couple years ago my Surface bricked itself one day.
So I bought a new one, fired it up, provided my MSFT login credentials and a few minutes later I had my entire system configured as a clone of the old one and my hard drive repopulated w links to all my cloud-stored files. Which over the next couple-few hours all downloaded and became local files.
With email it isn’t so much enshitification (though that has happened), but rather the whole GUIness of it all. I was happy with comp, scan, inc, show, and friends from mh. So simple, so fast, and so versatile. The insistence of email being more than just text put an end to that, though. I’m complaining about feature creep, I guess the great uncle of enshitification.
Former Netscape personnel developed Mozilla (which I used as a former Netscape devotee), and then Mozilla over time turned into Firefox, and eventually the Firefox people developed Thunderbird. (I was one of the earliest users of Thunderbird.) But it’s not like there is a direct line between the Netscape mail client and Thunderbird, and they are dramatically different products.
Code fragments, sure, the same way my car runs on ancient marine sea life that decomposed and over many years turned into crude oil. But you’re not going to actually find prehistoric sea monkeys anywhere in my car.
My understanding is that both Firefox and Thunderbird are something of a “Ship of Theseus” situation, where over time bits of code were replaced until at this point you probably won’t find much of the original Netscape code left anywhere, or at least not a significant amount of it.
Then again, Netscape introduced things like JavaScript and FRAME tags which are present all over the web (and web-based applications), so in a way, bits of “Netscape code” are in just about everything. Probably Outlook as well.