Take a look at
this thread over at the site you didn't get any response from. In particular, post #s 5, 6, 8 and 17.
This may answer what you are seeing, but I am not sure why the 8700 is getting all 90 days worth. Did that device actually have some of the old mail on it already? Do you have a storage folder that perhaps the 8700 is mapped to that the 8800 is not?
SteveTaz