Ah, now I understand your intention better. I though you want to draw a horizontal line between the times of Today, Yesterday, Last Week, 2 weeks ago etc. like M$ OutLook it does. What you want to have, is an additional column with some time indicator. Correct?
That's how I understood it, but I guess your interpretation might be more what Leho intended as they referred to time segments. In that case, I don't know of any way to do that in mutt.
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