The company I work for is big-ish, ~10k, and many use mutt, emacs, Thunderbird and some even use a mailing-list<->nntp with slrn.
I think it all depends on which area of work you are in. For software engineering folks it works just fine.
I for one use mutt and handle calendar invites with gcalcli, I can use LDAP lookup and HTML mails are converted using elinks and read inside mutt. If I want to see all the fanciness I just open the text/html attachment in Firefox.
They probably also use Outlook. That's what I do (4K employees). Used to use Mutt almost exclusively, but just became too hard and people complained about my emails turning everything to Courier. :)
I still use Mutt to quickly prune emails in the AM and for writing to mailing lists.
I've (sadly) gotten pretty used to Outlook and like it quite a bit. I do miss using vim to edit emails though...
I think it all depends on which area of work you are in. For software engineering folks it works just fine.
I for one use mutt and handle calendar invites with gcalcli, I can use LDAP lookup and HTML mails are converted using elinks and read inside mutt. If I want to see all the fanciness I just open the text/html attachment in Firefox.