bsd-mailx(1) on Linux
The text a6e198de891e, as Debian 6.0 (Squeeze) shipped it.
send and receive mail
Flags it lists
-
-E -
-I -
-N -
-a -
-b -
-c -
-d -
-f -
-i -
-n -
-s -
-u -
-v