Hi David,
This is progress. Now that we're getting a response from the server we know what to look at. We can see by the error that the email alias/forwarder/pipe is semi-operational, but needs some tweaking.
The error could be caused by one of the following:
1) The bounce.cgi script does not have 'executable' or '755' permissions as noted on
this help page.
2) The path to bounce.cgi is not correct, although it does look good: |/home/MYUSERNAME/public_html/cgi-bin/bounce.cgi
3) A call to the perl interpreter may be required. The alias might look like this:
|/usr/bin/perl /home/MYUSERNAME/public_html/cgi-bin/bounce.cgi
Set bounce to the first tick box = return to administrator and have yet to receive a bounce message.
When you send an email to a test list and -recieve- the message, check the headers/message source. You should see the "Return-path:" line with the bounce address or 'Administrator email' if bounce processing is disabled. Note that with bounce processing disabled it's a good idea to keep your 'Administrator email' on the same domain as ListMail is installed on to prevent authentication issues.
Please let me know if I can be of further assistance.
Regards