I think in system/core/pm/pm.list.inc.php we could create two categories in sent private messages list:
1) Sent but not already read messages (pm_state=0)
2) Sent and already read messages (pm_state=3)
Then, in tpl, we could distinguish them with a different status-icon...
What do you think?
in [color=#729FCF][b]BLUES[/b][/color] I trust