How numbers get flagged as spam

There is no single spam list. Each major US carrier runs its own analytics, often through a partner, and scores every originating number based on the calls it makes and how people respond. Phone makers and third-party apps add their own layer on top.

The scores are not shared with you. You find out a number is flagged when answer rates fall, when a prospect tells you, or when you call your own phone and see the label.

The exact models are private, but the inputs are well known. They come down to volume, pattern, and response.

• Volume: how many calls a number makes in an hour and a day. A number that goes from zero to two hundred calls in a morning looks like a robocaller.
• Duration: lots of very short calls. Hang-ups under ten seconds, unanswered calls, and calls that go nowhere all count against you.
• Rhythm: calls at perfectly even intervals, or many calls started at the same second, are a machine signature.
• Response: people reporting the number, blocking it, or declining calls from it. This is the heaviest signal and the hardest to undo.
• Ratio: outbound with no inbound. A real business number receives calls too.

The defence is to make each number look like a busy human, not a machine. That means three rules.

Cap each number per day. A human on a headset makes somewhere between eighty and a hundred and fifty dials in a day. A number doing more than that is asking for attention.

Leave a gap between calls from the same number. A few seconds is enough to break the machine rhythm. In parallel mode, use different numbers for the legs that start at the same moment.

Rotate across a pool. If a team of five makes six hundred dials a day, they need enough numbers that no single one carries more than its share. Spread the load to the least-used healthy number rather than always picking the best one.

Scores decay. A number that stops calling for a week or two often recovers on its own, as the negative signals age out. That only works if you have enough numbers to take one out of rotation without stopping the team.

Watch answer rate per number over a rolling window. When one starts to fall away from the others, rest it before it is fully flagged. Redialler does this scoring for you and marks a number as resting when it falls behind the pool.

1. Stop calling from it today. Every extra call reinforces the label.
2. Check the label yourself. Call a phone on each major carrier and see what appears.
3. Register the number. The Free Caller Registry and each carrier's own reputation portal let you tell them the number belongs to a real business.
4. Rest it for at least two weeks, then bring it back at low volume.
5. If it does not recover, release it and buy a fresh one. Do not release numbers you have called prospects from in the last month, since they may call back.

Registering the numbers you own before they are flagged is cheaper than fixing them after. Do it the day you buy them.