Judging from the amount of it the sending email portion is not what spammers struggle with. It's the "maintain your own IP with a great reputation" part. How would Postal help?
That's apparently a process that takes time, but in the long run it could easily pay off. Over the years I've dealt with "Verio" selling my ip address to spammers. Before that they had entire ranges of IP blocked that I got caught up in.
A couple years ago I did the work to use "Mandrill" in an app and they got merged with "MailChimp" who changed how my app could use their service and I had to redo those routines again.
Well from the install directions they recommend 8GB of memory for the server. A simpler SMTP server like Postfix or Exim can do with much fewer resources, and a spam operation doesn't care about abiding by protocol for redelivery attempts, they just fire and forget and mostly opt for direct SMTP delivery.