If you have a folder of email that needs to have the procmail rules applied, then the trick is to be logged in as the email user (which might involve editting /etc/passwd to give yourself access to a shell), and then position your self in the home directory, and then this works:
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If you have a folder of email that needs to have the procmail rules applied, then the trick is to be logged in as the email user, and then position your self in the home directory, and then this works: