Hi,
I've just upgraded to Courier-IMAP 2.1.2 from a version from a year ago. The upgrade went fine and the server works fine but I noticed that outgoing bandwidth usage is way up on the server. The old Courier would sit around 1 Mbps, the new is 5 Mbps for exactly the same user load. Stopping the server and moving back to the old version puts the outgoing bandwidth back where it was originally. Something in my installation is causing the server to use a ton of bandwidth, yet still apparently work fine.
Define 'bandwidth': that would be bandwidth as in bandwidth of IMAP collections to clients, or bandwidth as in 'NFS bandwidth'.
The only major change of note is the addition of custom IMAP keywords. The impact on IMAP clients should be minimal; it will results in a little bit of new traffic, but not that much.
Custom IMAP keywords do generate additional filesystem I/O. So the only thing that I can think of is that most of your IMAP clients can use custom keywords, if available on the server, and suddenly they see that they can, and go hog-wild.
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