Perpetuating bad UX choices (or at least trade offs made under the mobile constraint) from mobile into the desktop doesn't help anyone.
I use thunderbird because I want an email client, not a dumbed down web experience built for mobile.
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.
Its just yet another thing I shouldn't have to think about
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.