What is “internal ESP reputation” vs “ISP-level reputation”?

Internal ESP reputation is your standing within your sending platform:

ESPs track customer behavior and assign internal risk scores. High-risk customers may face sending limits, pool segmentation, or account warnings. This reputation determines your experience with the ESP.

ISP-level reputation is how mailbox providers like Gmail, Outlook, and Yahoo perceive your mail:

This determines actual inbox placement regardless of your ESP standing. A customer in good standing with their ESP can still have terrible deliverability if ISPs distrust their domain.

The two reputations are related but distinct. Good ISP reputation typically means good ESP standing. But ESP approval does not guarantee ISP approval.

Internal reputation is your rating with the shipping company. ISP reputation is your rating with port authorities. You need good standing with both, but they evaluate you on different criteria.