Something juicy about IP reputation. Most of us know by now that someone marking your emails as spam in their inbox negatively affects the reputation of the sending IP, that is why most people us ESPs.
Most of us also know that we can only send at certain volumes and speeds to ISPs before they get put out by our volumes and the volume tolerance levels depend on the reputation of the IP address.
We do not know enough about how any of this is actually calculated as the ISPs keep it pretty close to their chest to stop spammers finding way in.
Laura’s article is a lovely logical lesson about how the frequency of complaints within a given time might also be being used by the ISPs to measure and assign reputation. It may not be something that is fully actionable but the whole thing fascinates me and always makes me sound like I know a lot when I consult on deliverability! …have a read