Using Outlook client a rule is created and the setting is chosen to forward a copy of the item to another mailbox, the mail is forwarded to a different user in the source domain. User was selected from the target GAL.
Regular mail flow works fine, migrated user can send e-mails to source and target users and can receive e-mails from source and target users.
Missing (not activated) Exchange 2003 setting for Automatic Forwarding, which is disabled by default.
1. Start Exchange 2003 System Manager.
2. Navigate to Global Settings - Internet Message Formats.
3. In right window, right click on "Default" and select Properties .
4. On the "Advanced" tab, select "Allow Automatic Forward".
Even if a new user is created manually in target domain this users can not forward mail using a rule.