maildrop(1) on Linux
The text 3860c283b22f, as Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster) shipped it.
mail delivery filter/agent
Flags it lists
-
-D -
-M -
-V -
-W -
-a -
-d -
-f -
-m -
-t -
-w