If you're composing a new e-mail & using the 'Select Recipients' dialog,
clicking the sort arrow in the 'Name' header cycles thru FOUR options:
FullName ascending
FullName descending
Last, First ascending
Last, First descending
If a contact has a FullName/filename of 'LastName, FirstName', there is no
apparent difference. But if you allow the default FullName contruction of
'FirstName LastName', or if you edit FullName to be some arbitrary text, the
difference becomes apparent.
In terms of viewing the Contacts folder, the filename is governed by
'FullName' field of the Contact -- & the Contact Properites dialog
constructs 'FullName' as 'First Last' by default. If you click the
drop-list for the 'FullName' field, You are given 3 default contructions:
First Last
Last First
Last, First