After setting Exchange to Notes forwarding, all messages are returned as undeliverable with the following message:
A configuration error in the e-mail system caused the message to bounce between two servers or to be forwarded between two recipients. Contact your administrator.
This issue is caused because the forwarding address was set as the primary Namespaces (right side of email proxy). This Namespaces is shared between both source and target environments.
All forwarding should be set to the temporary sub-domain, not the primary shared Namespaces. When forwarding is set in Exchange, the targetaddress attribute is set with the smtp proxy or notes address of the notes recipient. If this proxy address is shared between the source and target mail systems, any mail forwarded through the notes connector will bounce back.
To correct this situation, temporary sub-domains should be in place in notes and in exchange and forwarding must be set to this Namespaces.