Hi there,
A few quick questions:
a) do you have shell/root access to the server on which you're installing osTicket? (handy for log checking)
b) do you get any bounce or failure messages when sending an email to the osTicket email address? If so, can you please paste the contents of one?
c) do you have "Admin Panel -> Settings -> Preferences -> Email Settings -> Mail Methods -> Enable email piping (You pipe we accept policy)" ticked?
d) which version of cPanel are you running?
e) what's the full contents of the forwarder you've configured?
f) have you tried inserting #! /usr/bin/php at the beginning of /api/pipe.php ?
This should allow us to figure out where things are going wrong
Kind regards,
Ebonhand