The should provide an API for that instead of implementing anything with Electron.
However, there is little movement in the desktop email app space anymore, so aside from their web app, I see no other clients supporting this.
Evolution added some nifty features lately (Markdown integration). And allows to use Client-Side-Decoration annd classic menus - usability wise awesome. Thunderbird got this year a complete redesign.
The other part are we as users.