exim+cyrus imap , pb of subfolder delivering...

[Erick Bullier]

I run Cyrus IMAP4 v1.5.19 with exim 3.35.
I would like to be able to send mail into shared subfolder, but exim say me 
all the time:
<toto+bulletin at mail.toto.com>: host mail.toto.com[195.xx.xx.xx] said:
    550 Unknown local part toto+bulletin in <toto+bulletin at mail.toto.com> 
Naturaly, the user toto exist and i can send to him mails...

I run exim with the director:
localuser_user_cyrus:
  driver = localuser
  transport = local_delivery_cyrus
#  suffix = .*

and the transport:local_delivery_cyrus:
  driver = pipe
  command = "/usr/sbin/cyrdeliver -m ${substr_1:${local_part_suffix}} \
             -- ${local_part}"
  user = cyrus
  group = mail
  return_output
  log_output
  prefix =
  suffix =

What is wrong, and what can i do?...

Thak's for your help,

E.Bullier