Chances are that it has been archived.
These files are not actually on your computer. Rather, GroupWise remembers where it stores each message and tells your computer which databases on the server to retrieve each individual file from. When you click to open a message or appointment, you are actually accessing a database on a server computer somewhere else on the Georgetown Network. After a while, these files pile up. When a group of messages are archived, a copy of it is stored in one of these two locations.