I have been using maildir as the message storage format for six months. I have known that the implementation is not complete and that there are several known bugs, so using it is risky. My reports that I have not experienced any problems may have encouraged other people to use maildir, so now I must report a problem. Twice recently, my IMAP inbox did not show all messages. Repairing the folder worked the first time. The second time, repairing the folder causes all messages in the folder to disappear. Worse, it seems that it deleted the inbox file in the file system. I do not know if this data loss was due to maildir. It may have been. I have returned to using mbox.