[Exim] Mail Trickling.

I have the following (legitimate) need:
To send large quantities of duplicated mails to individual addresses in
a given domain from time to time. (i.e. >50,000 users)

I was wondering what the best strategy was to implement this via a local
exim MTA.

or is this best done by trickling mail from the dispatching script to
the local smtp server?


Thanks,
Owen