The first vendor I found via Google offers 500 phone-verified gmail accounts for $150, so about $1.2M to fake all 4M users. At that volume you can probably get a discount and have them generate gmail addresses according to your specifications (to make them plausible matches for the rest of your fake data). Mix in some bought outlook accounts and some obscure domains you run yourself for extra plausibility.
Actually opening the emails without triggering Google is a bit more difficult, but I imagine a good residential proxy service (either legitimate or botnet) and a bit of scripting can solve that for another couple thousand USD.
Of course doing all of this makes you look more criminal and JPM look less dumb, so I'm not sure if this is actually a good idea even if you start off with the idea of defrauding the buyer.
