[Evolution] How to shrink mbox ?

[Carsten Zerbst <carsten zerbst groy-groy de>]

Hello, 

my Inbox (Display) usually contains less than 50 emails, 
but the mbox file contains ~5000 emails. The Properties on the Inbox
says the same. How could I force evolution to remove all emails not
displayed from the mbox ? A simple ctrl-e is obviously not the
answer ...

Thanks, Carsten