It is common when two companies merge that it is unlikely that they would be using the same type of mail system. In order to facilitate the changing of the domain name used by the second system to the domain name used by the GroupWise system, it will be necessary to route an inbound message to the system that is merging into the GroupWise system. The scenario will be similar to the one listed:
1. company abc.com buys xyz.com
2. abc.com uses GroupWise and xyz.com uses a different email system
3. xyz.com will be changing their domain name to abc.com, but will want to continue to use their own mail system until a migration is undertaken
To resolve this scenario, the best procedure will be to point the MX record for mail destined to abc.com at the GWIA that processes mail for abc.com. Within the GroupWise Administrator, the option to "Forward Undeliverable Inbound Messages to Host" should point at the SMTP server for the system that hosts xyz.com.
When an internet email message comes into email@example.com and 'user' does not exist in the GroupWise system, then the message is still accepted, but then it is forwarded to the host specified. If the message is addressed to firstname.lastname@example.org, then the message is rejected immediately by the GWIA since that domain name is not serviced by the GWIA.