User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:56.0) Gecko/20100101 Firefox/56.0 Build ID: 20171024165158 Steps to reproduce: Happens very frequently moving mails between IMAP folders belonging to different accounts and thus different servers. I've found no step sequence to surely reproduce. Happens more frequently with large mailboxes. Actual results: Selecting some message in the message list shows different message contents in the preview pane. Subject and senders are correct, but the contents are not. Usually they show some previous message on the same folder. I know that this can be fixed with a "Folder Repair", and I usually do that. The point is that I experience this problem every other day or more, and I think this reveals some subtle bug, maybe worth investigating. Expected results: Prevew pane showing the contents matching the message selected

Sadly there are a few reports of this kind, see meta-bug 714489.

We've just go another report on this and I actually have a reproducible case that corrupts my mailbox reliably. So let's do a forward dupe here. > Usually they show some previous message on the same folder. Indeed, that's what I see.