/var/qmail/bin/qmail-showctl will show you the running config.
Qmail does not allow you to restrict max recipients or max messages per session. I saw reference to a plugin to handle these controls, but do not know the name of it.
You can restrict max message size in /va/qmail/control/databytes
Example:
$ cat /var/qmail/control/databytes
10485760
That’s a 10MB limit
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