This is a reported issue here and there and so I doubt it is worthy of a bugzilla report, but I have yet to find a reliable solution. I list mail with newest messages on the bottom, just over the preview pane, so sort by date ⮟. When folders are recently repaired behavior is what I like: switch to folder and highlight and preview the newest (bottom most) message. Delete a message, highlight and preview the next more recent message in the list (highlight moves down one from the deleted message). After checking mail or other mailbox updates, whatever message is highlighted and previewed stays highlighted. I find this good and pleasing behavior. However, after some time, hours or weeks as described in other support requests/bug reports, this pleasing behavior changes and Thunderbird seeks the oldest message in the list, at the top of the list pane, which it highlights and switches preview to. This happens if I switch to the mailbox or if the mailbox is updated by checking mail or deleting a message. Since I background check, this can happen while reading a message (any message other than oldest) which is annoying. Reading is interrupted, I have grab the mouse and scroll back to the bottom of the mail list and select the newest (or whatever I was reading) again. The standard advice is properties->repair folder, which does work for a time, but not long, as others have found. https://www.reddit.com/r/Thunderbird/comments/tkpyx5/mail_list_keeps_jumping_all_the_upthe_earliest/ https://support.mozilla.org/en-US/questions/1231801 An option might be to delete the .msf files every night after verifying the screen is locked (so TB is not being used late) and keep them updated that way, but it would seem that preventing whatever is messing up the .msf files in the first place would be better. (I assume it is .msf corruption since "repair folders" works and that just deletes and rebuilds the .msf file). Any better ideas that that brute force hack?