I have an Exchange server 2003. I am hosting our company's website on one server hosted by Hetzner. This server is a web server. Plesk panel made default mail server as Postfix. The main.cf file contain relay server as our company's email server which is exchange 2003 server. In the main.cf file I put my exchange server as a relay host
relayhost = mail2.hassanabul.com\par
I send mail through psp command but when I send mail to other than my own domain, it fails and our barracuda device shows
Invalid Recipient (cuda_nsu 5.7.1 Unable to relay for firstname.lastname@example.org )
Any help will be appreciated.