Senders frequently request having their IPs added to our whitelist; if you're a sender who's interested in being whitelisted here, it's important that you read this section to understand what it is that we mean by whitelisting and what benefits you might gain from whitelisting.
First, it is not necessary to be whitelisted here in order to send mail to our customers. So long as your server's IP has valid reverse DNS and is not listed on any blocklist we use, mail from your server will be accepted here.
Next, whitelisting here just means that the rate at which we will accept mail from your server will be among the highest we offer; whitelisting does not mean guaranteed delivery to the Inbox here. Moreover, since our rate limits are based on an IP's previous history and reputation sending mail here, if your IP already enjoys a good reputation here, whitelisting may offer you no benefits in excess of what you already enjoy.
Last, management of our whitelist is handled by Return Path; we use their Certified program as the source of our whitelist, so if you believe you want to be whitelisted here, you should contact Return Path.