forwarding to many: will this work?

Got a file with, oh, let's say 40 addresses in it...
Will this work?
(or, if not, is there another way to do it within procmail, with out
calling anything besids sendmail?):

addresses = `cat addresses`

:0
* some tests
! $addresses

Also, in the addresses file: if this will work: what format is necessary?:

user1(_at_)host
user2(_at_)host

or:

user1(_at_)host,user2(_at_)host

Thanks

Luke