WttW: Why do you need so many IP addresses (part 2)

An interesting article from Word to the Wise about ESPs having a lot of IP addresses.
Why do you need so many IP addresses (part 2)

One thing I have found over the years is that an new IP is not good send large amount of email to straight away but it is relative straight forward, although tedious, to green it up. However, if you make one mistake ion the fist 12 months, you could be in the world of trouble.

Also large ISPS – Hotmail & Yahoo, tend to have IP reputation handlers to allow certain volumes in from an IP depending on it’s complaint rate – the rules in use for this are a very closely guarded secret.

Of course none of these rules apply if you pay return path to certify your emails, apparently?
Although the way that works is also a closely guarded secret, or maybe just from me!