I don't know if the CONDSTORE/QRESYNC issue has been fix or if maybe I'm connecting now to a different icloud imap server, but the problem seems to be resolved! I didn't note the version of the original server when I saw the problem, but the revision returned by imap ID is now "2204B190" and seems to work correctly. I still need to do more testing to make completely sure. There is still one issue that is not really CS/QR specific. I see this: 38 UID fetch 31:* (FLAGS) 38 OK FETCH completed (took 6 ms) According to RFC 3501, this should return the flags for the last UID message instead of returning nothing. See https://datatracker.ietf.org/doc/html/rfc3501#section-6.4.8: Also note that a UID range of 559:* always includes the UID of the last message in the mailbox, even if 559 is higher than any assigned UID value.

In case someone who works on icloud imap is reading this, there is one more thing I've noticed. The imap LANGUAGE command is advertised as a capability but it always fails like this: 27 LANGUAGE en-US 27 BAD Parse Error (took 0 ms) I've tried various other language code strings and even quoted the language code string and it makes no difference.

Thanks. I submitted the bug report here: https://feedbackassistant.apple.com/feedback/19553015