Sort and delete duplcate messages

I know that 'sortm -textfield Subject' will sort messages accoring to
the subject field. Having run that command, is there a way to then
delete the first duplicate of each message in the list such that if 1
and 2 are duplicates and 6 and 7 are duplicates you would delete messages
2 and 7 leaving 1 and 6?

Thanks