The comment " # Set IMAP_USELOCKS to 1 if you experience weird problems when using IMAP # clients that open multiple connections to the server. I would hope that # most IMAP clients are sane enough not to issue commands to multiple IMAP # channels which conflict with each other. " is actually somewhat disingenuous as it says that clients have to issue conflicting commands in order to be messed up. However, just having two sessions issue NOOP commands simultaneously while having the same mailbox selected counts as conflicting by this definition, and that is certainly not something I would think of to protect against as a client writer!

I would like to suggest that that option be changed to be on by default and have a comment such as # The IMAP_USELOCKS option should almost always be enabled. Only disable it # if you know that you will never have two connections open accessing the same # mailbox at the same time. Note that some clients (notably Outlook) do this # by themselves in the background so you might not know its happening.

This would probably remove the #1 issue people have with Courier imap, and make it more correct out-of-the-box.