qmail + throttling (limit bandwidth)

[Michael Maier]

How can I throttle the Bandwidth Usage with qmail ?
I have High Volume Server sending 3 Mio. e-Mails / weekly out.
My ISP bills in Bandwidth Consumation and that 3 Mio. e-Mails Send
produce very high Bandwidth Usage Peeks!!
Who can help?
PS: I'm on Sun Solaris 7 Box
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 With best Regards,
   Michael..