[exim] mail account followed by random number

Hi all

I have a router like so:
(got it from
http://www.exim.org/exim-html-4.50/doc/html/spec_46.html#SECT46.7)

account_bookings:
driver = redirect
check_local_user
file = $home/.forward
local_part_suffix = -*
local_part_suffix_optional
allow_filter

and a .forward like:

mail:/home/bookings# cat .forward
if $local_part_suffix contains -special then
save /home/$local_part/special
endif

I would like to receive emails for an email like:

booking-54423423@???

the number after the hyphen will be a random number.

Some one suggested I try the random number first, but I cant seem to
pull that off either

If anyone has any tips advice etc, it would be most appreciated.

Kind Regards
Brent Clark