[Exim] Use of "exists" in filter files

ok, I'm missing something here but I can't seem to get the format
right in using exists.

if exists "/etc/exim/var/daytime"
then

would seem to be logical but it doesn't work.

Ideas, pointers to the right part of the faq? ;)

-- 
The Flying Hamster <hamster@???>         http://hamster.wibble.org/
Discretion is the better part of Valor, and Cowardice the better part of 
Discretion. Therefore I'll be Valorous and run away.