Sadly, I do still use Yahoo. I fought moving to the updated version as long as possible, but I am dealing with the same growing pains as you.

On my email list, to the upper right, above the date column, is a button labeled "View." Under this is a pull down menu where you can choose where to have the preview pane (below or right are the options).

I am not sure what "in-line responses" are, so I cannot help you there. Good luck.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).