yeha its getting hard to deal with AOL/yahoo and comcast.

I was not familiar with senderscore.   Found this link https://www.senderscore.org/

What is the recommended process for "warming up" the new I.P. Address?

Douglas, from my reading you can warm up an IP manually by sending small amounts of e-mail and increment the volume each day until you reach your mail server's volume.  The 2nd option is to use vendor APIs, solutions, and services that will do this for you automatically.

It's really just one big pain in the ass!

If you have Windows on new environment then additional SmarterMail as outgoing gateway would be good solution IMHO.

SmarterMail as an outgoing gateway lacks proper IP rotation, so we use Ubuntu with Postfix for our outgoing gateways with IP rotation. If we add a new IP to the rotation we have some custom logic to prevent sending a zillion emails immediately off that IP.

What we ended up doing is using our old SmarterMail server as an outgoing gateway.

Now we are moving domains from the gateway slowly. Still seeing "deferred" errors on our new solution.

We are in contact with Verizon Media Postmaster via email and they are making changes to our new IP but stress that these changes take several hours to propagate.

Ron

Ron,

Verizon Media (Yahoo/AOL) have always been a problem for us with this. Recently, it took multiple conversations with Verizon postmasters to get it resolved, but all they revealed in the end was "Our engineers have found the issue and resolved it.". Which is true, we stopped seeing deferred messages immediately, but they didn't provide us a real answer.