[Exim] Mass mailing..

Hullo.. I have a need to do a mailing to about 7000 email addresses..
They are all in the same domain (our customers, specifically), but we
hope to implement a means for our customers to subscribe off-site
address and/or unsubscribe from the mailing, so they may not all remain
in the same domain..

What I've done in the past, is to break the addresses into groups of
20, and do an HBSMTP for each, eg

MAIL FROM: ....
RCPT TO: ...
RCPT TO: ...
RCPT TO: ...
(x20)
DATA
etc...

.. then put them all together, and pipe that into exim -bS with a HELO
and a QUIT stuck on..

The sticky point this time is that the message needs to be personalized
for each address, so instead of sending one message to 7000 recipients,
I am sending 7000 unique messages, each to one recipient.

I'm trying to figure out the most efficient way of dropping this into
exim's queue. Should I drop them in batches, adding a delay between
each, to avoid the 'queue_only_load', or will I do just as well to just
drop them all in as one, and let exim queue them up and run them out
after? Anyone have any other ideas?

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