Looks like the admin is missing in action. I just bought the plugin but I think I can answer your question. You’ll need to set up an email to use just for the email piping. I set one up called messaging@…. Here are the instructions from the documentation:

Please go to Front End PM > Settings > Emails > Email Piping.

Enable (It will add unique code in every message subject)
Set Piping Email which email you want to use
Clean reply quote Check if you want to clean quoted messages from email.
Make sure file wp-content/plugins/front-end-pm-pro/pro/fep-email-parser/email-piping.php has executable permissions. On Linux servers CHMOD this file to 755 (rwxr-xr-x).

Now copy real path from server of e.g. public_html/wp-content/plugins/front-end-pm-pro/pro/fep-email-parser/email-piping.php

Now

Log in to your cPanel
Navigate to Mail and select Forwarders
Click on Add Forwarder
Enter the Address to Forward (Set as Piping Email above)
Select Pipe to a program (you may need to click on Advanced Options to see the Pipe to a program option)
Enter the path you have copied above.
Click on Add Forwarder

Hope this helps.