I do not mess around with tabs or new windows to read my mail, but I find the feature works correctly with the reading pane in the main window (It is not a "preview" which a lot of folk assume.

So I guess the question is you read mail by displaying it where?

So I guess the question is you read mail by displaying it where?

I read mail in their own windows. I prefer dealing with mail in windows like the old days, and I don't really have the screen resolution to use the preview/reader/whatever pane in the main window even if I wanted to.

So, I guess this must mean that it's some bug where the setting applies only to the reader pane, and is not consulted for messages in their own windows. I cannot imagine this setting is truly intended to be ignored for mail in windows, as there's no real upside to that behaviour that I know of, and it goes against the grain of various older mail clients which have a similar "mark as read after..." setting.

See this other similar topic I just commented on https://support.mozilla.org/en-US/questions/1432464

See this other similar topic I just commented on https://support.mozilla.org/en-US/questions/1432464

Thank you for for your research. Unfortunately I don't think any of the referenced bugzilla tickets describe this problem exactly, though.

Please post your results with 115.5.2.

I apologize for the very long delay. Unfortunately it did not change anything.