[celsoazevedo]

It's hard to be in charge of a project like this. You're criticized no matter what you do.

The old UI was criticized by some for being outdated, a mix of old and new styles, didn't fit well with new OS/app styles, etc. It was crap. So they update the UI and it's still crap... for other users. Damned if you do and damned if you don't.

[blibble]

the people still using a fat client are likely doing it because they don't like change

edit: I say this MYSELF as a thunderbird user!

I don't want an "new experience" every 9 months, and having to explain it to my parents

[dubya]

Both outlook.office.com and mail.google.com use much more memory and CPU than any "fat" client, and are constantly changing little things about the UI. Safari now often closes outlook automatically on an M5 Mac because it's using significant amounts of energy.

[WD-42]

Or people that simply have more than one email account?

[brendoelfrendo]

And I use a fat client because I like having all of my email addresses aggregate to one place, and I like it when that software gives me a modern look and feel ¯\_(ツ)_/¯