New post-send hook. Though compose_sent could be a good hook name, it's too similar IMO to compose_send.

doc/Development/plugin.txt

@@ -307,6 +307,7 @@ but may be out of date soon thereafter.  You never know.  ;-)
   compose_bottom                 src/compose.php                 do_hook
   compose_button_row             src/compose.php                 do_hook
   compose_send                   src/compose.php                 do_hook
+  compose_send_after             src/compose.php                 do_hook
   folders_bottom                 src/folders.php                 do_hook
   help_top                       src/help.php                    do_hook
   help_chapter                   src/help.php                    do_hook