[exim] Configuring unauthorised sender responses

Greetings

We have been happily using exim on our mail servers for many years now but recently realised that some mail is being rejected due to response caching at our edge servers…

We use a simple list system (that I wrote a few years ago) which pulls data out of our HR database and creates files containing e-mail addresses (router described below) - which has an option to restrict the senders for submission to the list.
When a message is from an authorised sender it is delivered to the list - when the sender is not on the Allow list the message drops through to the next router and therefore ends up at the last router which has a ‘cannot_route_message’.

So far this sounds fine, the problem occurs when an intermediate MTA (e.g. our edge servers which I don’t control) tries to deliver a message with an unauthorised sender - this failure is then cached and no more messages to that list are accepted (even with authorised senders).

I expect I should be checking the senders in a different way and giving a different response code in cases where the sender is unauthorised - so that intermediate MTAs don’t cache the result for this recipient…

Does anyone have any pointers for me?

Thanks


Merlin



#### MBU Lists router ####
lists:
driver = redirect
# left 'domains' here in case we switch to a lists domain
domains = +local_domains
condition = ${if exists {MBU_lists_dir$local_part} {yes} {no} }
# this senders list checks for the 'allowed' file and if it does not exist allows any local sender
# e.g. /usr/lists/Allow.d/test-list
senders = ${if exists {MBU_lists_allowdir$local_part} {lsearch*@;MBU_lists_allowdir$local_part} {*@+local_domains} }
# e.g. /usr/lists/test-list
file = MBU_lists_dir$local_part
errors_to = MBU_postmaster
forbid_blackhole
forbid_file
forbid_include
forbid_pipe
one_time
retry_use_local_part
no_more


--
Merlin Hartley
Computer Officer
MRC Mitochondrial Biology Unit
Cambridge, CB2 0XY
United Kingdom