bsd-mailx(1) on Linux
The text ecd0c43065ad, as Debian 13 (Trixie), Debian 12 (Bookworm) shipped it. The page shows this text now.
send and receive mail
Flags it lists
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-- -
-E -
-I -
-N -
-a -
-b -
-c -
-d -
-f -
-i -
-n -
-r -
-s -
-u -
-v