This enhancement was submitted to the list a while ago. It lets vdeliver
used procmail on incoming mail if there is a .procmailrc in the
recipient home directory. The patch was modified slightly: procmail
will be used either if there is a .procmailrc in the home directory
or if there is a file /etc/vmail/domain.procmailrc. So you can turn
on procmail recipe's domain per domain without being forced
to have .procmailrc for each user.
Also, the control files used by procmail were moved from /etc
Check this out!