There's no such function as a standard part of Notes. Perhaps you came across it in someone's custom LotusScript code (e.g., the source for such a function is given in Notes/Domino 4 and 5 forum).
There also used to be a toolkit called DCO (Domino Collaboration Objects) to let VB code more easily manipulate mail and calendar functions in Notes, but I can't find out where to download the VB version -- only Java. Perhaps you can find someone who has a copy.
This was first published in June 2003