postfix and bulk email sending

Hi

I would like to know how to tune postfix for bulk email sending. I have to
send about 700.000 email to subscribers in as short as possible time. My
outgoing connection is 2,5Mb/s ( 300 kB/s), server have 256mb ram, and email
size is 150kb.

I wrote script, which injects about 1500 mails in 750 seconds intervals to
queue. I calculated this as 1500 mail * 150 kb / 300 kb/s = 750 s. This is
much more than enough, because this calculation doesnt take paralell
delivery into account.

Now I wonder about leaving this script and rely on postfix queue management
only. I plan to sort my recipient list by their domains, then make 70 copies
of email - each with 10000 Bcc recipients (I assume it iis
default_recipient_limit), then inject all this mails to queue.

Please send your comments and sugestions about this idea. How should I set
postfix parameters to send this mails as fast as possible?

Tomek