RT-Extension-CommandByMail-3.01: ProcessCommands subroutine undefined or missing

We are in the process of upgrading from RT 4.4.2 to RT 5.0.2, but are experiencing several problems with the CommandByMail extension in the newer version. Most notably, the extension cannot seem to find its own subroutine called ProcessCommands.

After manually downloading and installing the extension per the instructions at RT::Extension::CommandByMail - Change ticket metadata via email - metacpan.org and not running into any issues, we added the following lines to our RT_SiteConfig.pm for the extension:

Set(@MailPlugins, qw(Auth::MailFrom Action::CommandByMail));

We have also verified the installation was successful via the presence of the following configuration files:


Unfortunately, attempts at testing the extension using the specified commands from the CPAN page (e.g. Status: new, Priority: 1) continually result in the following error from our Postfix mail server:

(temporary failure. Command output: RT server error. The RT server which handled your email did not behave as expected. It said: Undefined subroutine &RT::Extension::CommandByMail::ProcessCommands called at /var/www/itrequests-d/local/plugins/RT-Extension-CommandByMail/lib/RT/Interface/Email/Action/CommandByMail.pm line 50. Stack: [/var/www/itrequests-d/local/plugins/RT-Extension-CommandByMail/lib/RT/Interface/Email/Action/CommandByMail.pm:50] [/var/www/itrequests-d/local/plugins/RT-Extension-CommandByMail/lib/RT/Interface/Email/Action/CommandByMail.pm:30] [/var/www/itrequests-d/sbin/…/lib/RT/Interface/Email.pm:428] [/var/www/itrequests-d/sbin/…/lib/RT/Interface/Email.pm:250] [/var/www/itrequests-d/share/html/REST/1.0/NoAuth/mail-gateway:61] )

If the extension has been fully installed, how is it that it cannot find its own subroutine?