mac mail sort by date newest at top by default
Solution 1:
If you change the sort by clicking on the table headers it should stay that way across launches.
Solution 2:
With the Date Sent column header is selected (blue), the default should be to sort with the newest at the top. If this isn't the case, click the column header again and the order will switch.
So, if it was oldest first before, it will now be newest first and vice-versa.