I think you've confirmed what I said in my parent comment...SES doesn't take a zero tolerance approach.
I think it is the shared IPs that I've blocked (54.240.27.189/24). You'll see they are on multiple blacklists.
If you really distrust mail from those IPs so much, why not just filter it straight to SPAM? At least you'd be delivering it and your users could whitelist senders (or domains) they trust.
For example, if you want a quota of 100 messages per day, you have to pay a one time fee of $.10 per message to get into the pool, so $10. If you want a quota of 50k messages per day you have to pay a one time fee of $.005 per message, so $250.
My good friend has worked on the email system for a mid-range consumer ISP for about the past 10 or so years. He told me 93% of all email they receive is spam. And they have a 60PB NAS for their mail store. So for every 1PB of storage they had to discard ~14PB of junk. And that’s just the stuff they summarily dismiss. Then some of the remaining 7% they accept makes it to your Junk folder.