I'm very happy that it's being updated.

Your comment maybe indicates the gray is too subtle, or invisible to users with bad eyesight.

Disagreed about the To/Cc redesign, the new design is much more efficient when you have multiple recipients, making good use of horizontal space. The old design did lead to:

1. Tons of wasted horizontal space (as each line is a recipient, on each line you only use the few characters describing each recipient, leaving space on the right blank). And also, one-line-per-recipient leads to tedious vertical scrolling inside a vertically-constrained space (3 lines by default, and you don't want more, you want to preserve vertical space for the email body, not the header).

2. Impossibility to easily copy/paste all recipients. With the new design, it's now easy: select all, copy (and repeat once if you have a Cc field, okay).

There's a reason this To/Cc design is what most (all?) desktop/mobile clients do.

I doubt there will be a single person for whom Thunderbird is their first email/messaging type app. Most would have used something on their iOS or Android devices first at least.

All of them will be comfortable with multiple users in a single To line, while having multiple lines for multiple users will actually appear alien to them.

This almost equals to assuming that nobody is older than 25 or 30 especially because the no "single person" assumption. I started with UNIX's mail in a terminal, used a dozen of different clients on UNIX, Windows, Linux, Android, not all of them graphical.

I've been using Thunderbird probably since its very first day. My other client is K9 on Android. I think the address pills will be OK but I want to test their manipulation with keyboard and touchpad.

I use thunderbird because I want an email client, not a dumbed down web experience built for mobile.

I mentioned mobile because as far as discoverability is concerned, there is an order of magnitude more mobile users than desktop users, so the vast majority of users will have no problem understanding this concept.

And if you've been a desktop user long enough that you havent used a smartphone then you're probably used enough software that have similar patterns (and used email enoguh) that you shouldnt have trouble realizing that single To line means you can add multiple recipients to the same line.

I've literally never used a mail client that didn't do multiple emails on the same line. On Desktop or Mobile.

And it's never been an issue.

As long as everybody is on your address book it's fine, but if they're not, things tend to get awry.

I haven't tried the new Thunderbird, but I am suspicious of this change as well.

This was my first reaction when I saw the change - I really hope they get this right as it goes to the core functionality of Thunderbird. If email addresses can't be easily and accurately edited in the To field, it will be a real problem for me.

I've used every major email platform and every single one manages to endure despite having emails on one line. Even Outlook does one line these days.

Its just yet another thing I shouldn't have to think about

You'd be wrong. I, grudgingly, moved from mutt to Thunderbird after it was clear that email was turning into MIME-encoded web pages.

Ironically, I am moving from Thunderbird to Mutt (NeoMutt actually). I find the elimination of HTML means it's actually easier for me to not get distracted by stuff I dont care about for email, which is interaction with real human beings, who are unlikely to be typing complicated HTML messages. Besides, with the right config (I'm still working on it), the HTML message is 1 shortcut away.

Back in my BBS days, there was ANSI color with IBM-extended (CP437) block graphics to liven things up, so I can see it has gone full circle a bit.

The old window was twice as big as it needs to be too, but I agree the new one is even worse.

I don't like the flat buttons either. I don't use macOS much, but the old ones with a subtle border look like they're native UI, whereas the new flat ones don't. A random image I found confirms that the old buttons and checkbox look the same as what the OS itself uses, while the new ones look very out-of-place:

https://i.stack.imgur.com/5ACES.png

Glad at least they've kept the (albeit small) separators between the buttons.

I immensely dislike the UI trend where everything is flat so there's no discernible separation between elements.

Yup, already hate it. I much prefer not looking through a list of buttons on the To line for the one I want to remove. Additionally, I can instantly see if I'm sending and email to my coworkers company or personal address without some damn tag after his name.

I know a few who swear by it