filter(1) on Linux
The text 8589575de634, as Debian 8 (Jessie), Debian 7 (Wheezy), Debian 6.0 (Squeeze), Debian 5.0 (Lenny), Debian 4.0 (Etch), Debian 3.1 (Sarge) shipped it.
filter incoming messages before adding to mailbox
Flags it lists
-
-S -
-c -
-f -
-l -
-m -
-n -
-o -
-q -
-r -
-s -
-v