smtpping(1) on Linux
The text 4d37dccb67f2, as Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch) shipped it.
SMTP benchmarking and measurement tool
Flags it lists
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-4 -
-6 -
-H -
-P -
-S -
-c -
-d -
-f -
-p -
-q -
-r -
-s -
-w