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Why A attestation doesn't stop Spam Likely

STIR/SHAKEN attestation A says who signed your call, not whether people want it. Why signed calls still get labelled, what A helps with, and how to check yours.

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An A-attested call can still show "Spam Likely". That surprises people who were told STIR/SHAKEN would fix it. It was never built to.

This page covers what the three attestation levels say, what they leave out, why labelling engines don't treat A as a pass, and how to see which level your own calls get. It ends with a checklist. For how the framework is set up on an outbound dialer, see STIR/SHAKEN for outbound dialers. For the level definitions in more depth, see STIR/SHAKEN attestation levels: A, B, C.

What does A, B or C attestation actually say?

Attestation is a signature on one claim: the originating carrier knows who the caller is, and says how far it will vouch for the number. A means the carrier verified the customer and that they have the right to use the number. B means the customer is known, but the number isn't verified. C means the call only passed through.

LevelCarrier is sayingTypical case
A"We know this customer, and they're entitled to this number."Your own DID on your own account
B"We know this customer. We can't vouch for the number."A number the account can't be tied to
C"We only passed this call along. We don't know the originator."Call arriving from a gateway or another network

Notice what each line is about: the carrier's knowledge of the caller and the number. That is a statement about identity. If you want the protocol background, read What is STIR/SHAKEN?.

What does attestation not say?

It doesn't say anyone wants the call. There is no field for "this person opted in", "this is a legitimate campaign" or "the last 400 people who answered didn't hang up". A well-signed call to a stranger who never asked to hear from you is still a call to a stranger who never asked to hear from you.

The consumer side is blunt about the result. Hiya's State of the Call 2026 reports that 86% of calls from unknown numbers go unanswered (12,000+ consumers surveyed in six countries). People decide on the screen in front of them.

Labels come from analytics engines, and those engines score behavior: call volume, call length, how often people answer, how often they report the number. Matt Florell, VICIdial's author, said in his 2021 Astricon talk that labels are based on the caller ID number. In the same talk he said "a minimum of 5 minutes and 200 phone calls can get you flagged". Neither fact has anything to do with a signature.

Why do signed calls still get labelled?

Because almost everything is signed now, and signing is not the same as being trustworthy. A signature that nearly all traffic carries can't separate good traffic from bad, so the engines have to look at other signals.

TNS's 2026 robocall report puts numbers on it:

  • 85% of Tier-1 carrier traffic was signed in 2025.
  • Of that signed traffic, 93% was signed at A.
  • Smaller carriers signed 17.5% of their traffic.
  • Up to 13% of traffic from invalid numbers was signed A.

That last figure is the one to remember. Traffic from numbers that shouldn't exist still got A on some of its calls. If the engines treated A as safe, those calls would sail through. So they can't, and they don't.

The practical reading: A is necessary and not sufficient. It is an input to a score, alongside everything the engine learned about that number from how people reacted to it.

What does A attestation help with?

It keeps you out of the starting hole. A call signed B or C, or not signed at all, arrives with less backing than an A call from the same number. Engines and receiving carriers can weigh that against you before a single person has answered.

We won't put a number on it, because we haven't measured one, and nobody who quotes a clean A-versus-B answer-rate gap on cold lists can show you the control group. The direction is clear, though. If your calls come out B or C when you own the number, fixing that is cheap and worth doing first.

It also makes you easier to reason about. When your calls are A and you still see labels, you know the cause is behavior and reputation, not signing. That narrows the search.

How do I see which attestation my calls get?

The signing happens at your carrier, after the call leaves your dialer. VICIdial itself never sees the verdict, so you won't find it in the admin screens or in its call logs.

There are two ways to find out.

  1. On VICIfast Voice, the DID Reputation Center shows how each call was signed (A, B or C), per SIP trunk and per number, next to the ring time and SIP result for that call. Nothing is installed on the box.
  2. With another carrier, ask them: "What attestation do outbound calls from my account get, per number, and can I see it per call in the CDR or the SIP trace?" A carrier that can't answer that has told you something.

If the answer comes back as a mix, sort the numbers by level. A B on one DID usually means that DID isn't registered to the account as yours. That is a paperwork fix, and nothing about dialing needs to change.

What if the same number is A on one trunk and B on another?

Then the trunks are signing differently. Attestation belongs to the call path, not just the number. If you send traffic to two carriers, or one carrier routes some calls through a downstream network, the same caller ID can come out at different levels.

Compare per-trunk results before blaming the number. In the Center, the trunk breakdown is where this shows up. Everywhere else, you are comparing carrier CDRs by hand. For passing your caller ID through to the carrier intact, see making sure your caller ID reaches the carrier.

Will the FCC change how A is shown?

Possibly. In October 2025 the FCC's Ninth Further Notice of Proposed Rulemaking (FCC 25-76) proposed showing a verified caller name alongside A-attestation indicators. This is a proposal. It isn't a rule, and nothing in this guide depends on it.

If it were adopted, the effect would run in A's favor: calls that are A and carry a verified name would look different on the screen from calls that are neither. It would still say who you are, not whether the call is wanted.

What should I do about it? A checklist

Work through these in order. The first two are signing. The rest are the behavior the engines score.

  1. Own the numbers, or hold the right to use them. A is a statement that you may use the number. Don't present a number you can't tie to your account. Under the Truth in Caller ID rule (47 CFR 64.1604) you can't send misleading caller ID with intent to defraud, cause harm or wrongfully obtain anything of value. Talk to your counsel about your own case.
  2. Get A where you can. Check every number on every trunk, as above. Fix B and C on numbers you own.
  3. Format caller ID the same way every time. Send the number in the form your carrier expects and stay consistent. See making sure your caller ID reaches the carrier and the FTC Caller ID Transmission Rule.
  4. Answer the callbacks. Telemarketers must transmit a caller ID that lets the called party make a do-not-call request during business hours (47 CFR 64.1601(e)). Put a person or an IVR behind every number you dial from.
  5. Keep volume per number sane. Spreading calls across a stable pool of numbers you own beats hammering one. Florell's 2021 observation - a number can be flagged after as little as 5 minutes and 200 calls - shows how small the trigger can be. VICIdial CID groups are how you spread it.
  6. Watch pick-up rates per number. When people stop answering a number, a label is the usual reason. The Center tracks how often a person picks up each caller ID, against your other numbers and that number's own history, and scores it. It infers a likely label from pick-up rates; it doesn't read carrier labels.
  7. Rest a number that drops. Rest it, don't hammer it. See How to rest a flagged caller ID in VICIdial.

For a deeper look at the labels themselves, read Spam Likely vs Scam Likely. For the dialer-side playbook, read Avoiding Spam Likely labels and STIR/SHAKEN and VICIdial.

What won't fix it?

Re-signing, re-registering or paying for a "better" attestation won't clear a label earned by behavior. Neither will a different carrier, if you send them the same calls at the same volume on the same number.

Florell said in that same talk that a label takes 2 to 21 days to clear after a number stops being used. Time and changed behavior do the work. We don't remove labels, file appeals, or whitelist numbers, and nobody can promise you spam-free numbers.

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