Hyperforce impact on email deliverability?

Hello friends. 

After migration to hyperforce all of the emails sent from service cloud appears to be blocked/blacklisted by a major email provider in Australia (bigpond.com). 

I am trying to figure out if it is just coincidence that we were blocked around the same time we were moved to hyperforce, or if it is hyperforce's variable IPs that caused us to be blacklisted. 

So, has this happened to anyone else?  thanks!!