How can I configure Exim to deliver to a Cyrus message store?

1. The reference manual contains an example that uses pipe delivery.

2. Here is a transport that uses LMTP delivery, assuming that $local___part contains the username:

cyrus_inbox:
  driver =lmtp
  user = cyrus
  socket = /var/cyrus/socket/lmtp

3. This is a transport that delivers direct to a non-inbox mailbox:

cyrus_mailbox:
  driver = pipe
  user = $local_part
  message_prefix =
  message_suffix =
  log_fail_output
  return_output
  command = "/usr/cyrus/bin/deliver -a $local_part \
             -m <mailbox-name> $local_part"

This delivers to the Cyrus mailbox user.$local_part.<mailbox-name>. Using user = $local_part and -a $local_part makes it work without needing an explicit p' ACL set for anyone' on the mailbox.