[exim] Bulk Outbound Performance

Good morning,

More to satisfy my own curiosity than anything else, I'm wondering about
the performance that could be squeezed out of Exim in a bulk mailing
capacity.

I have a client that currently uses and ESP who have an astounding
throughput of up to a million messages per hour. This brought up a
discussion about high-performance MTAs and tuning and the general
comments I'm hearing are that things like Exim, Sendmail & Postfix are
just not man enough for such a task and the absolute best you could
expect from any of them is about 100k messages per hour.

Now, I like to wipe out the fact from fiction because people like
PowerMTA are looking to sell their products and it would be in their
interest to neglect that any MTA (Exim/Sendmail/Postfix) could be set up
in a way that would easily rival their product.

Can anyone on the list tell me if it's possible to performance tune Exim
to a point where it could complete with this and possible strategies?

Kind thanks
Ron