smtp-source(1) on Linux
The text fd121ff6373b, as Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch) shipped it.
parallelized SMTP/LMTP test generator
Flags it lists
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-4 -
-6 -
-A -
-C -
-F -
-L -
-M -
-N -
-R -
-S -
-T -
-c -
-d -
-f -
-l -
-m -
-o -
-r -
-s -
-t -
-v -
-w