For the record, the solution I came up with was as follows:
# This router checks mails for a "Delivery-Age" header. If it exists
# and the actual message age is less than that specified in the
# header, mails are deferred until the next queue run, when they are
# tested again. When the condition is finally met, mails pass through
# to the smarthost router.
delay_until_delivery_age:
driver = redirect
domains = ! +local_domains
condition = ${if < {$message_age}{$header_delivery-age:}{yes}{no}}
allow_defer
data = :defer: Age now: $message_age Deliver at: $header_delivery-age:
no_verify
# All mails are routed to the Corporate mail-server for final delivery
smarthost:
driver = manualroute
domains = ! +local_domains
transport = remote_smtp
route_list = * 192.168.1.1 bydns
errors_to = $header_sender
Thanks again to the list and the Wiki
(http://wiki.exim.org/FAQ/Configuration_cookbook/Q9807)
Rgds,
Owen Boyle
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