ImailMsg obtains a file handle to the message from the \Exchsrvr\Vs1\Mailroot\Queue directory. This component also preserves P1 information as part of the message in a separate data stream.

When Exchange 2000 is installed, it adds another store driver (Drviis.dll). As a result, there is a pointer to the message in Web Storage System when the message goes to an Exchange 2000 recipient, or a file handle when the message goes to a drop directory.