Building on the work of Erwin Hoffmann and John Simpson here is a patch to netqmail-1.06 (with qmail-errmsg logging patch) to catch and disconnect connections that try to send SMTP commands before the SMTP greeting has been issued by the server.
Hello,
An Early Talker Patch is available.
I would not use such a patch, but here is the information for those who would like this feature.
-Raymond