LSUB always returns all the subscribed folders. For example lsub "" "test/*" returns a list of all the folders and not just subscribed folders that are subfolders of test. I.e, it returns the same folder list as lsub "" "*". For more details please see https://bugzilla.mozilla.org/show_bug.cgi?id=1817707#c15

I'm the IMAP maintainer for Mozilla Thunderbird. I've been looking into adding QRESYNC imap extension to Thunderbird which currently only supports CONDSTORE extension. The icloud server returns these in its capabilities response: CONDSTORE ENABLE QRESYNC indicating complete support for enabling CONDSTORE and QRESYNC. But when I try to enable them, I get no "ENABLED" untagged response as required by imap ENABLE rfc: Tbird sends: 33 ENABLE CONDSTORE QRESYNC UTF8=ACCEPT icloud sends: 33 OK ENABLE completed The correct imap ENABLED response is like this: Tbird sends: 33 ENABLE CONDSTORE QRESYNC UTF8=ACCEPT icloud sends: * ENABLED CONDSTORE QRESYNC icloud sends: 33 OK ENABLE completed Since icloud doesn't support the UTF8=ACCEPT imap extension, it should just be excluded from the untagged ENABLED response. Several other imap servers I've tested (Dovecot, Cyrus and Zimbra) respond correctly when Thunderbird attempts the ENABLE but icloud responds in a non-standard manner. There are other problems too with the icloud response to imap SELECT with the QRESYNC parameter in that it produces an imap FETCH response for all messages in the folder with a sequence number of minus 1 (sequence numbers are supposed to be positive, 1 to number of messages in folder, never negative). Note: This seems to require a tag. Couldn't find one relevant to my question so just picked one with "icloud" in name.