Exchange Server 2013 CU9 – Watch your IMAP clients
Great post from Frank Plawetzki (PFE) explaning that the Exchange CU 9 may create some issues in certain conditions with IMAP clients.
One of my customers was happily rolling out Exchange Server Cumulative Update 9 (CU9) on their servers, when help desk tickets started to arrive. IMAP clients were constantly prompted for their credentials and could not proceed past the logon prompt to their inboxes, despite correctly entering their credentials.
Read more at source: http://blogs.technet.com/b/mspfe/archive/2015/08/24/exchange-server-2013-cu9-watch-your-imap-clients.aspx