I'm genuinely curious; can you name a few more clients and features? A lot of the things you called out sound like "smart features" more than an overhaul to th

I'm genuinely curious; can you name a few more clients and features? A lot of the things you called out sound like "smart features" more than an overhaul to the app (or significant UI changes). I think a lot of the trendy email applications that came out around 2012 (Sparro and Mailbox), were really interesting, but niche. They've seemed to have all gone away and only nudged the email clients most people use everyday. I do like Gmails categorization, but I don't know of another client that does it. I also assume it requires a server-side component to look at and categorize email by looking at everyone's. Maybe it could work like spam detection? Again, it sounds difficult to get right--not just a design choice. Regarding the button size, looking at Google Inbox all of the buttons look proportional to me. Phones lend themselves to multiple rows of varying size icons. Desktops usually have a single vertical or horizontal row. Mixing up the size can waste space. It's funny looking back at screen shots from Thunderbird v1. It had a row of huge icons. They've since been replaced by smaller text-only buttons. Phone and web interfaces have less strict standards and consistency (which I think discourage a lot of people). I do think they could get rid of some clutter by ditching Chat, Address Book, Tags and Filters, and hide "Get Messages" under a mouseover (like Fastmail's client). Leaving "Write" on the left and and a text box for filtering on the right--perhaps ditching that whole row by integrating those two widgets into other places in the UI. But I also wouldn't mind if they improved the backend, added some of those "smart features" both you and I mentioned, and left the UI as it was years ago.