[n5bb]

After some testing, here is what I think is going on:

• Fastmail lets you set up any number of browser tabs and windows and mobile devices which are all looking at the same account. At any instant, each of these could be viewing the same folder, or different folders.
• Each instance (browser tab or app) maintains a local sort setting for each folder.
• So if you send a message which shows up in your Inbox, it might appear at the top of one instance while it appears somewhere else in the list of messages in another instance, depending on the local sort setting at that point in time. In other words, receiving a new message does not cause any change in the local sort order of any instance.
• You can not set a default global sort setting for a folder in some special setup screen.
• But a global sort order does exist at the Fastmail server for each folder. When you change the local sort order for a folder on a connected browser tab instance or a mobile app instance, the global sort order is immediately updated to your new sorting choice for that folder. If you then open a new instance of a browser tab or mobile app (which connects to the Fastmail server as it starts up), that new instance initially has no local sort settings for the folders, so it inherits the sort settings from the server.
• Now here is the tricky part. If you refresh the browser window, it's similar to opening a new instance, and the server folder sort order settings overwrite the previously set sort orders of the local folders.
• Changing what folder you are viewing does not directly cause the global sort order to overwrite the local sort order unless the browser data is stale and that window gets a refresh from the Fastmail server. I thing that the triggering event must be a JSON action which refreshes everything rather than just one folder.
• Refreshing the folder itself by using the three vertical dot ellipsis tool to the right of the folder name when performing a mouse-over then selecting Refresh only refreshes the messages being displayed and does not reload the sort order from the server.
• I don't believe that there is a specific time-out reset for the sort order. But it's possible that some system-wide operation at Fastmail might reset the sort order in all folders to "newest first". But I have seen no evidence of this myself.
• My guess is that you had changed the sort order for some folder from a different instance (perhaps the iOS app). Then after many hours when you looked at different folders, the local data was stale and the browser reloaded that window, which reset the sort orders to the global sort orders from the server (which had changed since your last use of that specific instance.

I hope this wasn't too confusing!

Bill