you can't configure IMAP email on macOS mail any longer without it phoning home to apple when you do so. i haven't inspected the traffic or binaries that do so, but if you want to configure imap email manually (or import a profile that does so) while blocking all communication to apple/icloud servers, macOS Mail.app won't work.

(edit: it works when installing via a profile, but only after some timeout/delay.)