It doesn't matter what you say

“What should we tell the ISP?” is a frequent question from my customers. The answer is pretty simple. It doesn’t usually matter what you tell the ISP. What matters are your actions.
If a sender is having delivery problems then the solution is not to call the ISP and talk to them about why the sender’s mail should not be delivered to the bulk folder. Instead, the solution is to evaluate the email and the address acquisition process and the list hygiene process. Identify where potential problems are and then resolve those problems.
Typically, the ISPs won’t need to be contacted. The changes to the email will register and delivery will improve. In some cases, particularly when there’s been some major mistake, contacting the ISP and explaining the mistake and what steps have been taken to stop the mistake from happening in the future may help resolve the issue faster. But if nothing has changed, then there’s no reason for the ISP to expect anything to change.
It doesn’t matter what you say. It matters what you do.