[Exim] Shadow Transport - procmail

I am using a shadow_transport to drop all incoming emails into a mailbox.
I have the transport defined as follows:

shadow_delivery:
driver = appendfile
group = Debian-exim
user = audit
mode = 0660
envelope_to_add = true
directory=/home/audit/Maildir
maildir_format

This works fine, but due to the high volume of emails I would like to use
procmail to filter the mail into folders. I have created a .procmailrc in
the audit user’s home directory, but this is not working. Is there anyway
to do this?

Also is it possible to have shadow transport like functionality on
outgoing emails?

Thank you