How can engagement or inactivity cause silent throttling?

Engagement-based throttling operates silently:

What ISPs track:

Open rates (with MPP limitations). Click rates. Reply rates. Move to/from spam folder. Time in inbox before deletion.

Low engagement signals:

Recipients ignore your mail. Messages deleted without opening. Long-term subscribers never engage. Mail sits unopened indefinitely.

ISP response:

Reduced inbox placement (more spam folder). Lower priority in inbox. Slower delivery. Eventually, increased rejections.

Why it is "silent":

No explicit bounce or error. Mail is "delivered" but not to inbox. Degradation happens gradually. Hard to detect without monitoring.

Prevention:

Segment by engagement. Re-engage or remove inactive subscribers. Send wanted, relevant content. Monitor inbox placement metrics.

Silent throttling is gradual quarantine. Your ship arrives, but cargo is diverted to the back warehouse.