Automatic
Generation of an Internet Address 
Use
As of 4.6C, a default domain can be specified for each client. This is used to automatically generate the Internet mail address of a sender whose address is not maintained in the central address management. The sender may be a person or a business object (such as a work item), for example.
This means, for example, that queries for a work item can be sent to a person in workflow and sent back by this person to the work item. The reply is then appended to the work item.
For more information, see the documentation on SAPconnect.