Few things damage an outbound team faster than every call landing as “Spam Likely.” The causes are usually fixable, but only once you understand what carriers are actually evaluating.

What STIR/SHAKEN does

STIR/SHAKEN is the framework US carriers use to cryptographically sign caller ID information, so a receiving carrier can verify a call’s origin has not been spoofed.

Signing happens at three attestation levels:

  • A (Full). The originating provider knows the customer and has verified their right to use that number.
  • B (Partial). The provider knows the customer but has not verified their right to that specific number.
  • C (Gateway). The provider has simply passed the call along and can vouch for nothing.

A-level attestation is what you want. It does not guarantee your calls are never flagged, but B and C attestation make flagging far more likely.

Attestation is not the whole story

This is the part that surprises people. STIR/SHAKEN verifies identity; it says nothing about whether your calls are wanted.

Separately, analytics engines run by carriers and third parties score your numbers on behavior: call volume, call duration distribution, answer rates, how often people hang up immediately, and how many recipients mark you as spam. A perfectly attested number with terrible behavioral signals still gets labeled.

Short average duration is the strongest negative signal. A number placing hundreds of calls that average eight seconds looks exactly like a robocaller, whether or not it is one.

Why legitimate numbers get flagged

The common causes, roughly in order:

Attestation below A. Often because the number was ported recently, or because you are sending a caller ID your provider has not verified you own.

Spoofing your own numbers incorrectly. Displaying a number your provider cannot verify drops you to B immediately. This is common when a business displays a main line number while calling from a different platform.

Too few numbers for the volume. Cycling a small pool of numbers through high volume drives per-number rates into robocall territory.

Short calls. Voicemail drops, wrong numbers and quick hangups all pull your average down.

Actual complaints. Recipients marking calls as spam in their phone app feeds directly into the scoring.

Fixing it

Confirm your attestation level. Ask your provider what level your outbound traffic signs at and why. If it is not A, the reason is the thing to fix.

Register your numbers. Free Caller Registry submits your numbers and business details to the major analytics providers. It is not instant and not a guarantee, but it establishes who you are.

Use branded calling where available. Displaying your company name and call reason on the recipient’s screen materially improves answer rates and reduces spam reports.

Right-size your number pool. Spread volume so no single number carries a robocall-shaped pattern. Match local area codes to the regions you are calling.

Fix the behavior underneath. Scrub disconnected numbers, honor do-not-call lists rigorously, and call at reasonable hours. Reputation scoring reacts to how recipients respond, so the durable fix is making calls people want to answer.

Remediate individual numbers. Each major analytics provider has a process to report a number wrongly labeled. Use it, but only after fixing the cause, or the label returns.

How long recovery takes

Expect weeks, not days. Reputation scores are built on rolling behavioral windows, so improvements need time to accumulate. Numbers that are badly burned are sometimes cheaper to retire than to rehabilitate, but retiring numbers without changing the underlying pattern simply burns the new ones too.