My experience having worked in several different jobs across several sectors, both in the public and private sector: email is still used heavily internally and it is the default for most people.

The formality of email has decreased over the years, though there’s still that odd expectation of salutations when writing emails. However, email has been around for most office workers entire working careers, and people don’t give up old habits easily. As is often said, “if it ain’t broke, don’t fix it”.

Another thing to note: many of the people I work with can’t even be reliably reached on something like teams. There’s no expectation that it must be monitored, but they are always reachable by email.