Clearing the FromDomain field

Scenario:I have 5 different Lotus Domino domains. One domain (/ABC) currently has an Inbound SMTP server that receives Internet mail, and routes it to the appropraite Domino domain. As well , domain /ABC also has an Outbound SMTP server that is uses to send email out to the Internet for all 5 domains. Once again, not problems.

Required:

In order to improve the efficiency of routing, and reducing network traffic, domain /XYZ would like to route email destined to the Internet via it’s own Domino server. I have made the appropriate configuration changes. During my testing, from a client in domain /XYZ I sent an email to an external account. I could see it was sent directly (and not longer through the Outbound SMTP server in domain /ABC). During my next test, I sent an email to a user in the /XYZ domain from an external source. The message was picked up by the Inbound SMTP server in domain /ABC, and sent to the user in /XYZ. When the user replys to this email, it sends it back out through domain /ABC instead of directly through the Internet.

I have done investigation in to this, and it appears that the FromDomain field is set to be domain ABC before sending it on to the user in XYZ. I have tried placing an agent in the mail.box of the server on domain XYZ to blank the FromDomain field on all inbound email but that does not appear to work.

Is there a way that the FromDomain field can be set with out having to modify any templates? Any help would be appreciated.

Thanks.