cyrus-smtptest(1) on Linux
The text 18836973f1f7, as Debian 12 (Bookworm) shipped it.
Cyrus IMAP documentation Interactive SMTP test program. This is actually installed as a hard linked copy of imtest(1). It allows you to authenticate and send SMTP commands to the server.
Flags it lists
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-I -
-X -
-a -
-c -
-f -
-i -
-k -
-l -
-m -
-n -
-o -
-p -
-q -
-r -
-s -
-t -
-u -
-v -
-w -
-x -
-z