Barracuda SPAM & Virus Firewall 200 - Remote Oulook users unable to send email. Action is Blocked. Reason is Invalid Domain

I have recently implemented a Barracuda SPAM box in a hosted environment for my customers.  Basically, my customers sit behind their own IP address in each of their offices.  Some of these IP addresses may point to their actual domain and others may not.  The ones who do not get the following error message from Outlook:

Your message did not reach some or all of the intended recipients.

      Subject:      mail test
      Sent:      7/14/2014 9:01 PM

The following recipient(s) cannot be reached:

      user@somedomain.com on 7/14/2014 9:01 PM
            Server error: '550 No such domain at this location'

On the Barracuda, in the Message Log, the Action is Blocked and the Reason is Invalid Domain and their IP address "in this example" is an IP address from Grande Networks a local ISP.

I realize that the Barracuda is denying their SMTP connectivity due to the fact that their from domain in the email address does not match the Grande Networks IP address.  To resolve this problem, I tried adding the domain name in the Block/Accept -> Sender Filters "Allowed Email Addresses and Domain" but I got an error message "Whitelisting your own domain not allowed".  This is because I configured under the IP Basic -> IP Configuration "Domain Configuration" the Accepted Email Recipient Domains" with their domain.  Not sure what to do from here to get this to work properly.  Any ideas are greatly appreciated.