My cron job didn't work so I searched the forums, and found another 1and1 user.
This thread, http://osticket.com/forums/showthread.php?t=14046(http://osticket.com/forums/showthread.php?t=14046), suggested that 1and1 only offered PHP-CGI,( not PHP-CLI, ) which didn't work with cron.php
That thread linked to http://osticket.com/forums/showthread.php?p=37198(http://osticket.com/forums/showthread.php?p=37198) and in #2 of that thread Peter said to rename rcron.php.
I don't know if what has been said above is correct, which is why I'm trying to understand what I've done, and how it works.
John