You can specify which column you want to sort on by clicking the appropriate column heading.
Another way to specify which column to sort on is to choose the column at "Sort on" in the pane'sview properties.
There are a few sorting rules to note:
If you sort on
FirstClass does this
Name
Sorts items by the name of the sender (for incoming messages) or receiver (for outgoing messages).
To reverse the sort order of the column on which you are sorting, click the column heading.
You can also reverse sort order by selecting "Reverse sort" on the View Properties form. Top
Showing the newest item first
To make items appear from newest to oldest, select "Show newest items first" in your preferences. Top