I found this in developer guide:

If it can find a match, it is considered Resolved. It will create an Address object
from the information provided. This Address object is listed in the “Address”
property of the Recipient object. If GroupWise cannot find a match, then
GroupWise determines if it is an internal recipient by checking the value of the
EmailType property equal to the string “NGW”. If the address is internal,
GroupWise sets the Resolved property to egwNotFound or egwAmbiguous.
Note: This search order of address books can lead to problems of personal address
books containing entries of users who have been deleted, or migrated to other
post offices. Also, groups might contain users in address books that have already
been searched. A useful workaround is to always specify the System address book
as the book to resolve to. To access the system address book, use the
Account.SystemAddressBook property.
The Recipient object also has a property called “TargetType” of an enumeration
type which indicates whether this recipient is a primary recipient (egwTo), carbon
copy recipient (egwCC), or blind copy recipient (egwBC).
Other property values of the Recipient object are duplicated in the Address object,
such as DisplayName, EmailAddress, EmailType, Parent, and Application. Unlike
the Address object, the first three of these properties are read/write. Should some
of these values be changed, the “Resolved” property will automatically be reset to
egwNotResolved – since no verification has yet been made the new property can
be resolved.
The Recipient object also has a method called “Delete” which will allow this
Recipient object to be deleted.

I seem like if you pass "egwCC" as the parameter, it might work.