[exim] Need hints on how to require a file before local deli…

I have localuser: using mysql lookup for path. I use Maildir and have
it auto create directory.

The lookup is something like:
directory = ${lookup mysql { select concat('/mail/', domain.name, '/',
account.login, '/Maildir/') as directory from domain join account on
(account.domain_id=domain.id) where domain = '${quote_mysql:$domain}'
and account.login = '${quote_mysql:$local_part}' and ( domain.active=1
and account.active=1 ) } }

I deliver all email to a shared /mail/ mount point for example:

/mail/joe.com/jason/Maildir/

/mail/ is a shared filesystem mount point so I'd like to check for
/mail/.mounted before deliverying to disk or I'll end up delivering to
/mail/ locally and really messing things up :)

/mail is owned mail:mail as well as all files under /mail/*

Thank you in advance.

Lanny Jason Godsey