I've been using the same email app for the last 10 years: Netscape Navigator Version 3.0 Gold (? 1994).
Go ahead and laugh, but I think it's the best! It's so prehistoric that the modern day exploits or bugs can't penetrate it - because it simply ignores any routines it doesn't understand (which is generally anything besides text and basic html).
Even if a malicious hacker could generate something to fuck with it, would he waste his time on a program that is used by only a handful of people in the entire wolrd? Hell, I might be the only one who still uses it. That's something I should look into.
As for a browser, it's not very good. It can't read modern scripts, protocols, etc. Most tables don't even show up.
The WYSIWYG html editor is still rather handy. When I'm really lazy, I just open it up and cut and paste things around. So simple to use.