[Exim] how to disable dns queries for sender addresses

i've got fetchmail working with exim to get mail from my isp. then my imapd
feeds the mail from var/mail/$user to ~user/INBOX.
it is all working fine, however if i recieve several messages at once, exim
pauses do deliver the mail, starting again later. but the timeout for my inet-
connection is set to one minute, so eventually when exim tries to deliver the
mail, the connection is down and dns lookups fail. since all sender
verification is already done (by my isp), and exim will never recieve mail
directly, i figured i could turn off dns lookup completely (for senders of
course).
HOW ??
roaming through the faq and archives i wasn't able to figure it out by myself.
below you wil find a copy of my exim.conf (stripped #'s)
-----------
domainlist local_domains = @
domainlist relay_to_domains =
hostlist   relay_from_hosts = 127.0.0.1:172.16.4.0/24
acl_smtp_rcpt = acl_check_rcpt
rfc1413_query_timeout = 30s
ignore_bounce_errors_after = 2d
timeout_frozen_after = 7d
begin acl
acl_check_rcpt:
  accept  hosts = :
  deny    local_parts   = ^.*[@%!/|] : ^\\.
  accept  local_parts   = postmaster
          domains       = +local_domains
  require verify        = sender
  accept  domains       = +local_domains
          endpass
          message       = unknown user
          verify        = recipient
  accept  domains       = +relay_to_domains
          endpass
          message       = unrouteable address
          verify        = recipient
  accept  hosts         = +relay_from_hosts
  accept  authenticated = *
  deny    message       = relay not permitted
begin routers
dnslookup:
  driver = dnslookup
  domains = ! +local_domains
  transport = remote_smtp
  ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
system_aliases:
  allow_fail
  allow_defer
  data = ${lookup{$local_part}lsearch{/etc/aliases}}
  file_transport = address_file
  pipe_transport = address_pipe
userforward:
  check_local_user
  file = $home/.forward
  no_verify
  no_expn
  check_ancestor
  file_transport = address_file
  pipe_transport = address_pipe
  reply_transport = address_reply
localuser:
  driver = accept
  check_local_user
  transport = local_delivery
begin transports
remote_smtp:
  driver = smtp
local_delivery:
  driver = appendfile
  file = /var/mail/$local_part
  delivery_date_add
  envelope_to_add
  return_path_add
  group = exim
address_pipe:
  return_output
address_file:
  driver = appendfile
  delivery_date_add
  envelope_to_add
  return_path_add
address_reply:
  driver = autoreply
begin retry
*                      *           F,2h,15m; G,16h,1h,1.5; F,4d,6h
begin rewrite
begin authenticators