This question shows how far we’ve travelled from the original concepts of sending/receiving/viewing email. I just found it funny that you said “regular HTML client”, as if that was the default interface for email. Originally, it was all text, so this post is in many ways closer to how many thought of a “regular” client. But ever since Hotmail, it’s been a gradual shift away from command line email towards web applications. Desktop GUIs are still (kind of) holding on, but even they are more likely than not to be an Electron app.

To answer your question, these days, I’m not sure. There are so many extra features that email providers (Gmail/Office365) include in their web interfaces, it’s hard to not make the argument that the web interfaces are the better way to use email.