Anybody know of a SMTP relay program that allows setting up multiple IP pools for relaying outgoing emails and can cycle thru them the list of IP's. Trying to keep from getting messages about too many messages  coming from a single IP and rejected emails from some of the big ISP's (Like yahoo). We handle a lot of mail and some customers have large mailing lists. All are valid emails, but sometimes the sheer number causes issues. Been looking around and haven't seen anything. A windows program would be preferred but a linux product would be OK too. I'm sure others have run into such and issue and curious as how you handled it.