I'm still seeing this (or similar) bug on Debian Bullseye (both main w/ 3.2.x and backport with 3.4.x). In a telnet session, if I Select Inbox and then issue Idle, imapd will respond with + idling, but then when new mail arrives there is no notification. With debugging enabled I can see idled sending the notification to imapd, but imapd does not send notification to client. Also for whatever reason, any attempt at continuation (Noop or Done) results in an error, though it does seem to jump out of the Idle.
