In my website (under development), the members can send messages to each other which are sent directly to their email, now I'm worried that some members can send spam to other members (I have a spam filter but it doesn't give 100% protection as you know), I'm worried that my domain might get blacklisted on Yahoo, Gmail, Hotmail or AOL which will cause any messages sent from my domain to end up in the spam folder, this is why I want to add the domain of my website to their whitelists (if they exist).

P.S. I don't want to use private messages that members check on the site and I have my reason for this.

Thanks