Every send to a dead address is a small vote against your sender reputation, cast every single day.
Across eight datasets, teams that synced one global suppression list to every vendor cut hard bounces by a third within a month.
The surprise was the second-order effect: complaint rates fell too, because chronic complainers were finally suppressed everywhere at once.
Dead addresses cost twice — once in fees, once in reputation. You pay the vendor for the attempt, then you pay again when receivers log that you attempted it. At 1.8M emails a month, a suppression list that lags behind reality is a recurring subscription to looking sloppy.
The operational half of the fix is unglamorous: one global list, propagated everywhere, fast enough that a new entry lands at SendGrid, SES and TEM within thirty seconds. The boring infrastructure is the multiplier — hygiene stops being a quarterly cleanup project and becomes a property of the routing layer itself. Nothing about it shows up in a demo. Everything about it shows up in the bounce rate.