[Exim] scanning virus

Hello,

I'm using exim as a MTA to deliver local mail, as well as external mail. I
pick external mail from our ISP
with fetchmail.

I succesully set up amavis to scan all mail (internal and external) with :

#                      DIRECTORS CONFIGURATION                       #
scanmails: (1rt director)
  condition = "${if or {{eq {$received_protocol}{scanned-ok}}} {0}{1}}"
  driver = smartuser
  transport = scanmails_pipe

#                      ROUTERS CONFIGURATION                         #
vircheck: (1rt router)
  condition = "${if eq {$received_protocol}{scanned-ok} {0}{1}}"
  driver = domainlist
  route_list = "*"
  transport = scanmails_pipe

#                      TRANSPORTS CONFIGURATION                      #
scanmails_pipe:
  driver = pipe
  bsmtp = all
  batch_max = 32767
  command = "/usr/sbin/scanmails -f ${sender_address} -d
${local_part}@${domain}"
  prefix =
  return_output = false
  return_path_add = false
  user = amavis
  group = mail
  path = "/bin:/sbin:/usr/bin:/usr/sbin"
  current_directory = "/var/tmp"
  headers_add = "X-AntiVirus: scanned by AMaViS (http://amavis.org/)"

Every things ok except : if i send a mail to 10 users, the mail is scanned
10 times. No matter for a small load, but
i'm afraid of the behaviour now the load is growing !!

Is there something i'm missing ?

Thanks for any advices

Pascal