@canadaduane I stand corrected. libcamel is actually now part of e-d-s and it includes email support although there is still quite a lot left for clients to implement. That's probably what is used here.
Nevertheless, it's great someone is experimenting with a modern UI on the top of Evolution codebase. We've been trying to modernize the UI, but it's challenging. Evolution has a large base of long-time users who are used to the UI.