From Xojo Documentation
Resets the mail server to the state that it was when you logged in.
RollbackServer can be used to undo deletions that occur by accident. The changes aren’t committed until the connection is closed. RollbackServer will roll back changes that have not yet been committed by issuing a RSET command to the POP3 server (see RFC 1939 for more details).
On success, the RollbackSuccessful event is fired. Otherwise, the ServerError event is fired.