Package: cyrus-imapd Version: 2.5.10-3 When using Apple Mail (version 10.x or 11.x) against a Cyrus imap server, it seems that Apple mail does not properly implment the IDLE command. After a day or so, we have seen that many idling imapd processes are created, exceeding the maximum number of child processes that cyrmaster will spawn, preventing any new client to connect to the mail server.
It seems that upstream cyrus has made a patch for this behavior at https://github.com/cyrusimap/cyrus-imapd/commit/865199dce1291c612c5b5f3f5957b7800ba863b9 for the 2.5 branch. We have this patch running locally and it seems to fix the problems mentioned above. I am running Debian Scratch version 9.2, updated from Jessie
