The app in question, is independent of LXDE, but I know some distros will include an e-mail app with a particular desktop environment. GTK2 has been around for a long time and wasn't sure if it was eventually going to be deprecated in favor of GTK3.
As it currently is, LXDE works perfectly.
The e-mail app would crash, regardless of what desktop was used, because it is a library that is part of X11 causing the crashes. At the time, I didn't know exactly what was causing them, until I ran gdb to get a backtrace from it.
I upgraded to Fedora 33 last night and oddly, the e-mail app hasn't crashed yet.
Revisiting LXDE
Re: Revisiting LXDE
Debian Sid - LXDE