I have a client who is using Interspire e-mail marketer to send out his e-mail messages, and this guy sends something like 100,000 e-mails per session and does this around 3-4 times per month.
He's one of my hosting clients, and I'm trying to throttle the messages he sends out, so that some ISP's (like Yahoo! for example) don't start rate limiting him and classifying him as a spammer.
His FBL e-mails come to me (abuse@), I've applied for whitelisting with most of the ISP's (AOL, Yahoo!, etc) or their FBL if they don't utilize a whitelist. I've even managed to get him listed at DNSWL.org (they wouldn't accept him at first since he had no mailing history).
I also setup a proper rDNS PTR record, setup his SPF record, and DomainKeys signature signing on all his outbound e-mail messages.
So now, I just want to know how to rate limit his outbound messages directly on the server.
I'm highly proficient with SSH and can manipulate cPanel config files if necessary.