[Exim] .forward permissions

Exim 4.32 on Alpha Tru64 5.1B

As part of a biannual cearout of 'deadusers', such users
have their home directories disabled for a while, in an
attempt to warn other users of their files. This is done
by removing all access permissions from their home dir.
No other permissions are changed.

If such a disabled user has a .forward file, exim still tries to
make use of it, despite a router like:

userforward:
driver = redirect
domains = @
check_local_user
file = $home/.forward
no_verify
no_expn
check_ancestor
# allow_filter
file_transport = address_file
pipe_transport = address_pipe
reply_transport = address_reply

Shouldnt the

file = $home/.forward

line fail and cause the router to decline? Or does exim distinguish
between 'permission denied' and 'doesnt exist'? Should I be using a
different test here?

I dont think this problem occurred with exim 4.30 but I cant be sure
since we only do this thing every 6 months, and I've moved to 4.32
since the last clearout.

Cheers,
Terry.