Never heard of this concept in my career. We learned the hard way this weekend.
If moving a pre-existing SmarterMail solution to a new IP address, one should "warm up" the new IP address.
We migrated Saturday night around midnight. We immediately saw blocks from AOL, Yahoo, and Comcast. They seem to rely on our IP SenderScore (Return Path) which was null.
This morning around 11am, our SenderScore came online at 81/100. Our old mail server SenderScore was 97/100.
We are still seeing delays. However, I have noticed gates opening slowly. Today was a busy day for us. A lot of apologizing.
We did 500 things Saturday night. 1 thing we did not do is "warm up" the new IP address.
Now we know and hopefully now more of you know.