IMAP IDLE
https://discussions.apple.com/thread/2547839
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Disabling IDLE in courier-imap.
I had a similar problem with Apple Mail which has a configurable setting to use the IMAP IDLE functionality to stay logged in, periodically checking email. As the server in question was primarily used by Mac users, this caused imapd to run out of daemons and stop responding. One solution is, of course, to raise MAXDAEMONS in /etc/courier-imap/imapd, but you will eventually begin to tax your server's resources unduly.
The better solution is to disable IDLE entirely in /etc/courier-imap/imapd.
Change:
IMAP_CAPABILITY="IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA IDLE"
To:
IMAP_CAPABILITY="IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA"
... and restart courier-imap. This should prevent those pesky Blackberry (or Apple Mail) connections from persisting ad infinitum.
Hope it works for you!
Franklin
