Barracuda Bouncing Emails
Solution 1:
The Reporting-MTA has tried to send a message to the Remote-MTA which has rejected the message with an error described in Diagnostic-Code.
The error 550 Sender IP reverse lookup rejected is most likely related to SMTP Reverse DNS Resolution which is further related to a Reverse DNS Mismatch test.
Solution 2:
550 Sender IP reverse lookup rejected
You need to have your ISP create a PTR record for your mail server, for the IP you are sending mail from.