[exim] How can I distinguish between files and directories u…

Hi,

I'm starting to use exim to replace an outdated qmail installation, and
it works fine up to now. I am handling multiple domains, and I thought I
could choose this directory layout:

for mailboxes:
     /var/mailboxes/$domain/$local_part/{new,cur,tmp}

for redirections:
     /var/mailboxes/$domain/$local_part
     (a regular file containing the redirections)

In the routing section of the configuration file, I tried to separate
these things apart using require_files:

for redirections:
     require_files = !/var/mailboxes/$domain/$local_part/.
for mailboxes:
     require_files = /var/mailboxes/$domain/$local_part/.

This setup would ensure that no user can have both a mailbox and a
redirection at the same. But when I looked at the exim source code, I
figured out that exim tries to be too clever for me, and that it treats
all errors except ENOENT as a fatal failure. (For redirections, the
error is ENOTDIR.)

Is there some clever way to keep my directory layout?

Roland