If your calls are getting marked "Spam Likely" by day three of a push, STIR/SHAKEN is probably part of the story. You don't need to become a telecom engineer to fix it — but you do need to know enough to ask your carrier the right questions before you burn through a block of numbers.
Here's what attestation actually is, why it matters for campaign-scale dialing, and what to demand from whoever is terminating your calls.
What STIR/SHAKEN actually is
STIR/SHAKEN is the framework U.S. carriers use to sign outbound calls so the receiving carrier can tell whether the caller ID is legit. Every call your dialer puts out gets stamped with an "attestation level" by the carrier that originates it. That stamp travels with the call and influences whether T-Mobile, Verizon, or AT&T show it as a normal call, a warning, or block it outright.
There are three levels. In plain terms:
- A (Full): The originating carrier knows who you are and confirms you have the right to use the number you're calling from. This is what you want.
- B (Partial): The carrier knows who you are but can't confirm you own the specific number. Common when a dialer uses numbers from one provider but terminates through another.
- C (Gateway): The carrier just saw the call come in from somewhere and is passing it along. Treated with suspicion by downstream carriers.
B and C calls are more likely to get flagged, labeled, or outright blocked by the terminating carrier's analytics. A calls aren't magic — they can still get flagged if your behavior looks like spam — but you're starting from a much better place.
Why this matters more for campaigns than for a normal business
A plumber making forty calls a day with a signed A-attestation number doesn't have a deliverability problem. You do, because:
- You're pushing thousands of calls per hour in a short window.
- You're calling cold lists where recipients don't recognize the number.
- You're often rotating through dozens or hundreds of DIDs.
- Spam analytics (Hiya, TNS, First Orion) weight velocity and answer-rate heavily. One bad day tanks a number.
If those calls are going out with B-level attestation because your dialer and your DID provider are different companies that don't talk to each other, you're starting every call on defense. Pair that with a 2% answer rate on a cold list and the carrier's spam engine labels the number inside 48 hours. We go deeper on that cycle in how campaign numbers get flagged and blocked.
The question that matters: who is signing your calls?
This is the single most useful thing to ask a prospective termination carrier:
"If I bring my own DIDs, or buy DIDs from you, what attestation level will my outbound calls get signed with — and under what conditions does that drop?"
The honest answer is usually some version of:
- Buying DIDs from the same carrier that terminates your calls: A-level, assuming you're a known customer in good standing.
- Bringing DIDs from a third party: B at best, often C, unless the carrier can verify ownership via a signed delegation or hosted arrangement.
- Spoofing numbers you don't own: C, and you deserve it.
This is why consolidating your bulk DID purchase and your termination with one provider matters more during a cycle than it does for a steady-state business. Split them and you fight the attestation problem on every call.
Attestation is necessary but not sufficient
Here's the honest nuance: A-attestation does not guarantee your calls land clean. It gets you to the starting line. What happens next depends on:
- Call velocity per number. If one DID dials 400 calls an hour, analytics will flag it regardless of attestation.
- Answer rate and short-duration ratio. Lots of 2-second calls (voicemail, hang-ups) look like a spammer confirming live numbers.
- Complaint rate. One voter hitting the "report spam" button on a Pixel phone matters more than you'd think.
- CNAM and branded caller ID. Separate from attestation but reinforces trust. Covered in CNAM registration for outbound numbers.
So attestation is table stakes. Pacing, list hygiene, and number rotation are the actual game. If you're sizing a dialer plan, our notes on sizing DID blocks for your call window are a decent starting point.
What to put in your carrier evaluation
When you're on a call with a termination vendor, run through this list. Don't accept hand-waving.
- Confirm attestation level on calls where you own the DIDs through them. Get it in writing or in the MSA.
- Ask what happens if you bring external DIDs — can they host or delegate so you still get A?
- Ask about their relationship with the big three terminating carriers. T-Mobile and Verizon treat upstream carriers differently based on reputation. Your attestation can be perfect and still get downgraded in reputation scoring if your carrier is on a bad list.
- Ask how fast they can rotate numbers if a block starts getting flagged mid-cycle. Hours matter.
- Ask whether they offer any kind of reputation monitoring so you know a number is going bad before your agents are hearing dead air all shift.
There's more on structuring that conversation in choosing a SIP termination carrier and the political dialer deliverability checklist.
Common misconceptions worth killing
"We're A-attested so we're fine." No. A-attestation keeps you from being disadvantaged. It doesn't override the carrier's spam analytics. You still need to pace, rotate, and clean your list.
"STIR/SHAKEN doesn't apply to political calls." It applies to every call. Political speech has protections under the TCPA; it has none under carrier analytics. T-Mobile doesn't care that you're calling to turn out voters.
"If we just use a lot of numbers, it doesn't matter." Rotation helps, but if every one of those numbers signs at C, you're just burning through them faster. See rotating flagged numbers for how to do rotation right.
"The carrier will tell us if there's a problem." Most won't. You find out when answer rates crater.
What to do next
Before your next push:
- Pull a sample of outbound calls from the last cycle and ask your current carrier what attestation they signed at. If you can't get a straight answer, that's your answer.
- Decide whether your DIDs and your termination are coming from the same shop. If not, understand what that costs you per call in deliverability.
- Build a reserve of fresh, unused numbers before the surge, not during it. Mid-cycle provisioning is painful — see emergency number provisioning.
- Get on a call with a vendor who will actually explain their signing posture. Ask for the rate sheet and the attestation terms in the same conversation.
Attestation is one piece of a bigger deliverability puzzle, but it's the piece most campaign managers don't ask about until it's too late. Ask early. Get it in writing. Then focus on the parts you can actually control day-to-day — pacing, list quality, and how fast you can swap a bad number for a good one.