Emails bounce back when CloudLinux's CageFS is enabled

Symptoms

When a user has CloudLinux's CageFS enabled with an autoresponder or is piping emails to a script, you encounter an error(s) similar to the following examples:

CONFIG_TEXT: You are not authorized to run this command

CONFIG_TEXT: 1e7jB9-005Fzw-OF ** |/usr/local/cpanel/bin/autorespond username@domain.com /home/user1/.autorespond (username@domain.com) <username@domain.com> R=virtual_aliases_nostar T=cagefs_virtual_address_pipe: Child process of cagefs_virtual_address_pipe transport returned 1 from command: /bin/cagefs_enter 

Cause

There are a few different reasons this can happen.

Resolution

CloudLinux provides the following article, which covers this in great detail:

Emails Bounce Back when CageFS is Enabled