If it is blocked by your clients’ infrastructure, it is not passing the test.
Unless this is a hill you want your business to die upon, finding another email service might be a better option. Changing your business practices is probably within your control. Changing another business’s business practices probably is not.
Good luck.
Our emails go through all providers and land in inbox except when they are fronted by proofpoint.
I read the OP’s description of what they send to customers inboxes and it is exactly the sort of email I mark as spam. In a corporate environment, it is exactly what I would expect a paid spam filter to filter.
Yeah it’s crazy. Large established entities rarely if ever get preferential treatment or make the rules outside of the internet.
If I were you, I’d expend a ton of time and energy trying to win this battle.