If you are constantly getting this error message in Mutt (seemingly every time Mutt checks for new messages, or you change folders), then I may have a solution for you. You see, when I tried to lookup this message, I found two things:
- Pages saying the message was harmless and to be ignored
- Pages giving a technical explanation of the error message (which also tend to fall in the first category too)
Two pages in particular are this one from the Pine users group, and this one from the IMAP FAQs which give technical explanations. Basically, the UID’s must be increasing in a mailbox, and someone detected a dis-order. Typically, clients take the opportunity to re-order the UIDs to correct the problem.
But in my Mutt instance, this persisted restarting the client, moving messages, and more. I could not get the message to go away. After understanding the technical side, I went to find the problem. But I couldn’t find it. It did not occur in the mailboxes themselves.
Finally, I realized it had to do with the header cache. I deleted the header cache, and now I don’t have the error message anymore.