> In order to send large numbers of emails from an IP address -- you need to gradually ramp up number of emails sent
As a spammer you would not go for dedicated IP; you would rather want to use a shared pool as pissing in a big pool plenty of people who hold their liquids to themselves will help your pee to be less visible and detectable.
Here are samples of my spam box from this week so far, courtesy of Sparkpost (their complaint/spam/abuse mailbox is probably going into null, as I have never received a single response and majority of spam I see these days comes from them)
cristo.cumplirmideseo.com mta609d.sparkpostmail.com
diana.unavidaprospera.com mta678b.sparkpostmail.com
michele.felicidadyprosperidad.com mta717d.sparkpostmail.com
alexa.umavidaprospera.com mta678b.sparkpostmail.com
to.believeinmyfuture.com outbound40.sparkpostmail.com
These are shared pools and finding abusers is harder when you stay in large pool.