Earlier quoted context omitted.
New Outlook still doesn't handle S/MIME. That means it's between annoying to useless in large companies, depending on the volume of such e-mails you're getting.
What email client is popular in large enterprises then? Last time I worked in a company like that it was all microsoft software, including outlook, by policy
Here's the thing though: Microsoft is rather heavy-handed about pushing "New Outlook" and "New Teams". New Outlook is mostly just a wrapped webapp - so slightly cleaner than the old one, but otherwise much slower and less functional. Now, guess which Outlook has had support for Copilot for the past couple months? :).
Right now it's mostly an annoyance - I have to switch back and forth couple times a day, depending on whether I need "snooze e-mail" or S/MIME at any given moment. But the latter is really a dealbreaker. Strange for a product sold to corporations, which makes me think that MS is planning to get people off e-mails entirely.