[exim] reusing existing smtp connections

Hi list,

I'm running a mailman-based listserver. One of the lists contains a
rather large number of recipients for the same domain. The list is
configured in a way, that creates a new message for every recipient
(e.g. "personalize").

When a mail is sent over this list, exim creates a new smtp connection
for every mail it gets from mailman. This causes the recipients' server
to start rejecting connections as we reach it's connection limit. The
remaining mails are queued for later delivery. On every queue run, a
bunch of messages to this domain is delivered until my server hits the
connection limit again.

The situation is even worse because the target domain's servers use
greylisting. So a good part of the available smtp connections is used
without a successful delivery attempt in order to update the domain's
greylisting database.

Is there a way to configure exim in a way, that it reuses smtp
connections to deliver multiple mails for the same domain in one
connection? Is this possible with immediate delivery or only from a
queue run? What do I have to configure to get this?

I already found connection_max_messages but as it is set to 500
(default) in my trnasport, there seems to be something else missing. I
also tried to set remote_max_parallel to more than the default 2, but
queue runners still open a new connection for each message in the queue.

Best regards,
--
Joint Administration
Information Services & Technology
Patrick Cernko