Contributed Patches:

qmail has many patches contributed by open source world.
Check the http://www.qmail.org/top.html

I included just followings:

qq-custom-error-patch.diff: Allows you to define custom smtp errors.

qq-patch.diff: Allows you to execute a binary specified by the QMAILQUEUE environment.

qsheff-patch.diff: Mixed version of above two patches. Allows you to define
custom smtp errors and executing bin/qmail-qsheff directly as qmail-queue.

-b$

