How do ESPs typically handle suppressions?

Your Email Service Provider (ESP) does a lot of work behind the scenes to keep your suppressions from accidentally getting mailed. Understanding this helps you work with your ESP more effectively.

When you upload a list or segment your audience, your ESP compares every recipient against your suppression file. Any address on your suppression list gets automatically filtered out before the send. You might think you're sending to 50,000 people. Your ESP silently removes 2,000 suppressions and actually sends to 48,000. You only see and pay for the actual send count.

But here's where it gets interesting. Many ESPs maintain their own global suppression lists. If one customer on their shared IP pool hits a spamtrap, the ESP often suppresses that address for all customers. Why? Because if the whole IP pool gets blacklisted, everyone on that IP suffers. The ESP is protecting you from other senders' mistakes.

The same applies to spam complaints reported through Feedback Loops. Some ESPs add high-complaint addresses to a shared block list so nobody on that IP accidentally mails them again. It's a reputation defense mechanism.

What you need to know: Your suppressions work at two levels. Your account-level suppressions (your uploads, your bounces, your unsubscribes) filter before every send. Your ESP's global suppressions add an extra layer of safety. You can't see all of the ESP's global suppressions, but you're protected by them.

This is why staying on top of your own suppressions matters. The faster you suppress a hard bounce or complaint yourself, the faster your ESP can use it to protect its network.

Next step: Check your ESP's documentation on how suppression filtering works, and ask them whether they maintain a global suppression list for shared IP pools. It's worth knowing.