STIR/SHAKEN Explained: What Outbound Teams Need to Know in 2026
STIR/SHAKEN is call authentication that shapes outbound answer rates. Learn attestation A/B/C, why calls get spam-labeled, and what outbound teams should do.
Quick answer
STIR/SHAKEN is a caller-ID authentication framework that cryptographically signs outbound calls so receiving carriers can verify the calling number is legitimate. It assigns an attestation level — A, B, or C — that feeds carrier and third-party analytics. For outbound teams, weak attestation makes calls more likely to be flagged "Spam Likely," which lowers answer rates.
Your outbound team can run the best lists, the best agents, and the best pacing logic and still lose the moment your calls display as "Spam Likely" or "Scam Likely" on the recipient's handset. A growing share of that outcome traces back to a single behind-the-scenes signal: how your calls are authenticated under STIR/SHAKEN.
Most agents and even many managers have never seen STIR/SHAKEN directly, because it happens at the carrier layer in fractions of a second. Yet it quietly shapes whether your number rings clean, rings labeled, or is dropped to voicemail by the recipient's carrier before a human ever decides. For BPOs, collections agencies, telecom resellers, and sales teams making high call volumes, understanding this framework is no longer optional.
This article explains what STIR/SHAKEN is, how attestation levels A, B, and C work, why authentication connects to caller-ID reputation and spam labeling, and — most importantly — the practical steps outbound teams should take in 2026 to protect answer rates.
What STIR/SHAKEN Actually Is
STIR/SHAKEN is a pair of technical standards for authenticating caller identity on IP-based phone networks. STIR (Secure Telephony Identity Revisited) defines how a call's origin is cryptographically signed. SHAKEN (Signature-based Handling of Asserted information using toKENs) defines how carriers deploy STIR across the real-world telephone network.
In practice, when your call originates, the carrier that hands it into the network adds a signed SIP Identity header to the call setup. This header is a digital signature — backed by a certificate — that asserts two things: the calling number is real, and the originating carrier has some level of confidence in the caller's right to use it. As the call crosses to the recipient's carrier, that carrier verifies the signature and reads the assertion.
In the United States, STIR/SHAKEN implementation is mandated under the FCC's rules stemming from the TRACED Act, which is why calls in and out of the US market are routinely signed and verified today. Other regions have introduced analogous caller-authentication frameworks on their own timelines. If you dial into the US market, this framework is directly relevant — see our overview for outbound teams calling the US for market-specific context.
It is important to be precise about what STIR/SHAKEN does and does not do. It authenticates who is calling and whether the number is legitimately theirs. It does not, by itself, decide that a call is spam, block a call, or apply the "Spam Likely" label. Those labeling decisions are made by carrier analytics engines and third-party reputation databases — but attestation is one of the strongest inputs those systems consume.
How Attestation Levels A, B, and C Work
The heart of SHAKEN is the attestation level, a rating the originating carrier assigns to each call based on how confident it is about the caller and the number. There are three levels, and the difference between them can materially affect how your calls are treated downstream.
| Attestation | Name | What the carrier is asserting | Typical outbound impact |
|---|---|---|---|
| A | Full attestation | The carrier knows the caller and can confirm the caller is authorized to use the calling number. | Best case — least likely to be treated with suspicion, all else equal. |
| B | Partial attestation | The carrier knows the caller but cannot confirm their right to that specific number. | Weaker signal — more exposed to analytics scrutiny and labeling. |
| C | Gateway attestation | The carrier passed the call along but has no direct relationship with the caller. | Lowest confidence — most vulnerable to flagging and reduced trust. |
The key takeaway: attestation is assigned by the originating carrier, not by you and not by the destination carrier. You cannot self-declare Level A. You earn it by having a legitimate, verified relationship with the carrier that originates your traffic and by demonstrably owning or being authorized to use your calling numbers. This is why the way you source and configure your numbers matters so much.
Why Attestation Alone Is Not the Whole Story
A common misconception is that Level A guarantees your calls will never be labeled. It does not. Attestation is an identity signal, not a behavior signal. A number can be fully attested as Level A and still get labeled "Spam Likely" if its calling behavior looks abusive — extremely high velocity, very short call durations, low answer rates, or spikes in consumer complaints. Conversely, weak attestation makes it easier for analytics engines to treat borderline behavior as suspicious. Attestation and behavior work together.
Why Calls Get Labeled "Spam Likely" or "Scam Likely"
The labels recipients see on their screens are produced by analytics engines and reputation databases operated by carriers, handset makers, and specialized reputation providers. These systems combine several inputs to score each call in real time. Authentication is one input; behavior and history are others.
- Attestation level: Lower attestation lowers baseline trust and raises the odds that other risk signals tip a call into a label.
- Calling velocity and patterns: Dialing a very large number of destinations in rapid sequence from one number resembles robocalling.
- Answer and duration signals: Numbers that are rarely answered, or that produce mostly very short calls, accumulate negative signals.
- Consumer complaints: Manual spam reports from recipients are a strong negative input across the ecosystem.
- Historical reputation: A number that was previously abused — even by a prior owner — can carry a poor reputation into your hands.
Because labeling is behavioral and cumulative, the same number can move from clean to flagged over days or weeks if it is overused or misused. This is the direct bridge between authentication and reputation, which we cover in depth in our guide to caller-ID reputation for outbound teams.
The Caller-ID Reputation Connection
Think of STIR/SHAKEN as the front door and caller-ID reputation as your standing once you are inside. Good attestation gets your call taken seriously; healthy reputation keeps it that way. Neither is a permanent guarantee. A well-attested number with abusive behavior degrades. A number with a clean history but weak attestation is more exposed to scrutiny.
For outbound teams, this means two problems must be solved at once. First, an identity problem: make sure your calls are properly authenticated and attested through carriers that recognize you and your numbers. Second, a behavior problem: make sure your dialing patterns, number usage, and volumes stay within ranges that analytics engines read as legitimate business calling rather than robocalling.
What Outbound Teams Should Do in 2026
You cannot directly control what attestation a carrier grants or what label an analytics engine applies. But you can control the conditions that make good outcomes far more likely. Here is a practical checklist.
1. Get Your Numbers Properly Registered and Verified
Work with carriers and SIP providers that support proper caller registration so your traffic can qualify for full attestation. Provide accurate business identity information and keep it current. The more clearly the originating carrier can tie your numbers to your verified business, the stronger your attestation posture.
2. Practice DID and BYOC Hygiene
Treat your DIDs (direct inward dialing numbers) as assets with health, not disposable throwaways. Key practices include:
- Warm up new numbers gradually rather than blasting maximum volume on day one.
- Rotate numbers thoughtfully to distribute volume, without churning so fast that it looks evasive.
- Vet numbers you inherit — a reassigned number may carry a poor prior reputation.
- Match local presence honestly to legitimate business need, not to disguise your identity.
- Retire and remediate numbers that pick up persistent negative labels.
If you bring your own carrier, disciplined BYOC configuration lets you keep the carrier relationships and number ownership that support strong attestation while running your dialing on modern software.
3. Monitor Caller-ID Health Continuously
You cannot fix what you cannot see. Monitor how your numbers are being displayed and treated across major carriers, watch answer-rate trends per number, and act early when a number starts to degrade. DialerBee's caller-ID intelligence is designed to surface this kind of visibility so teams can respond before a slow decline becomes a hard collapse in contact rates.
4. Keep Behavior Legitimate
Align dialing velocity with human-scale outreach, honor do-not-call and consent obligations, keep call content relevant to the reason you are calling, and give recipients clean opt-out paths. Sustained legitimate behavior is what preserves the trust that authentication opens the door to.
Remediation: When a Number Gets Flagged
Even careful teams occasionally see a number get labeled. Remediation is a process, not a switch. Start by confirming the label is real and identifying which carriers or reputation providers are applying it. Many providers offer registration or dispute channels where you can assert legitimate business use and request a review. Where a number is genuinely damaged, the pragmatic path is often to rest it, reduce its volume, or retire it and shift traffic to healthier numbers while you correct the underlying behavior that caused the label. Fixing labels without fixing the behavior behind them tends to produce short-lived results.
How DialerBee Helps
DialerBee is built for outbound teams that live or die by answer rates, so caller-ID health is treated as a first-class concern rather than an afterthought. Through caller-ID intelligence, teams get visibility into how numbers are performing and being treated, so degradation can be caught early. Flexible DID management supports warm-up and thoughtful rotation as compliance-supporting controls rather than blunt number-churning.
For organizations that want to retain their own carrier relationships and number ownership — a foundation for stronger attestation — DialerBee supports bring-your-own-carrier (BYOC) configurations. And because outbound teams increasingly operate across markets, DialerBee's language-aware AI supports 9 languages (English, Arabic, Spanish, French, Italian, German, Turkish, Hindi, and Urdu), helping multilingual teams keep both authentication hygiene and conversation quality consistent. Results vary by market, carrier, and configuration, and outcomes observed in selected pilot conditions may differ from your own.
Frequently Asked Questions
Does STIR/SHAKEN block spam calls?
No. STIR/SHAKEN authenticates the calling number and assigns an attestation level, but it does not block calls or apply spam labels on its own. Blocking and labeling decisions are made by carrier analytics engines and third-party reputation databases, which use attestation as one input alongside calling behavior, complaints, and historical reputation.
Can I choose my own attestation level?
No. Attestation is assigned by the carrier that originates your traffic, based on how confident it is about your identity and your right to use the calling number. You cannot self-declare Level A. You improve your attestation posture by using carriers that recognize you and by properly registering and owning your numbers.
Why do my calls show "Spam Likely" even with full attestation?
Full attestation confirms identity, not good behavior. A Level A number can still be labeled if its calling patterns look abusive — very high velocity, mostly short calls, low answer rates, or a spike in consumer complaints. Attestation and behavior are evaluated together, so both must stay healthy to protect answer rates.
How does BYOC affect STIR/SHAKEN attestation?
Bring-your-own-carrier lets you keep direct carrier relationships and clear number ownership, which are foundations for stronger attestation. Because the originating carrier can more readily tie verified numbers to your verified business, disciplined BYOC configuration can support better attestation outcomes, though the final level is always assigned by the carrier, not the dialer.
Does STIR/SHAKEN apply outside the United States?
STIR/SHAKEN is mandated in the US under FCC rules stemming from the TRACED Act. Other regions have adopted analogous caller-authentication frameworks on their own timelines. If your team dials into the US market, STIR/SHAKEN is directly relevant regardless of where your team is located, so US-bound traffic should be authenticated accordingly.
What should I do first if a number gets flagged?
Confirm the label is real and identify which carriers or reputation providers are applying it. Many offer registration or dispute channels to assert legitimate business use and request review. In parallel, reduce or rest the number and correct the underlying behavior that caused the flag, since fixing a label without fixing behavior usually produces short-lived results.
This article is for general informational purposes and is not legal advice. Regulations and carrier policies change — consult qualified counsel and your carriers for your specific situation.