Email piping problem for some servers.

Hi,

I've set up a catch-all email account that pipes into a PHP file - lets' call this *@test.hello.com which pipes to |/home/test/test.php

While majority of the servers work when you send to hello@test.hello.com. Some servers have their emails sent to hello@test.hello.com bounced.

Why would there be a 550 error when it's suppose to be a catch-all address?

Could it be because of qmail? I don't have experience with qmail, but servers that worked used postfix when sending the emails.