As of 4:4.5~20100912.1174548-1maemo1.1173569 , in the email-list view, emails are always sorted by date. From time to time I like to sort my emails by other criteria (esp. author and size). Also, I like to invert the order sometimes (oldest first, smallest first etc). There is no (obvious) way of doing that.
Implemented in revision 1200974.
version: 20101202-1202744-1maemo1 Under Actions/Messagelist Display Format it is possible to change the sorting.