[exim] Fastest way to send multiple messages?

Hi list;

Few days ago i started creating a newsletter program that should send
the same mail to multiple users.
But because we are talking HUGE amounts of mail (60,000 mail addresses)
i thought to ask your opinion
of what would be the smartest and fastest way to do this (mails should
leave in 2-4h).

First i tought of creating mails straight to exim spool directory, but
had lots of trouble to create em without
exim saying: "Format error in spool file 1EwKaG-0002Dj-OV-H: size=855"
or something like that.

Then i tought of sending mails via perl script using sendmail. But is
this opinion fast enough.

The problem of this is that it is pretty hard to test this program
because i just cant send test-messages to
60,000 users.

Hope you can give me some clues on how to continue with this project.

Thanks.

Juuso Töytäri