[Exim] unknown local-part

Hi *,
I'm trying exim 3.30 and cyrus-imapd 2.0.16.
I can't deliver messages on my local machine.
Debugging exim I get the following: unknown local-part in domain.
local_user_cyrus director skipped: suffix mismatch.

What does this mean?

This is the snippet of the director:

local_delivery_cyrus:
  driver = pipe
  command = /usr/cyrus/bin/deliver \
            -m ${substr_1:$local_part_suffix} -- $local_part
  user = cyrus
  group = mail
  return_output
  log_output
  prefix =
  suffix =

Thank you,
Toni