STIR/SHAKEN explained: caller ID authentication for outbound calls

If your team makes outbound calls and you have noticed more of them showing up as "Spam Likely" or going unanswered, STIR/SHAKEN is part of the story. It is the industry framework built to authenticate caller ID and fight illegal spoofing — and it directly affects whether your legitimate calls reach people. This guide explains what it is in plain terms. It is general information for outreach teams, not legal or engineering advice.

What STIR/SHAKEN is

STIR/SHAKEN is a caller ID authentication framework. The names are acronyms for the underlying standards (Secure Telephone Identity Revisited and Signature-based Handling of Asserted information using toKENs), but the idea is simple:

• When a call is placed, the originating carrier digitally signs the caller ID with a cryptographic certificate.
• When the call reaches the terminating carrier, that carrier verifies the signature to confirm the caller ID was not spoofed in transit and to see how strongly the originating carrier vouches for it.

The goal is to make it much harder for bad actors to fake the number showing on someone's phone — the tactic behind a huge share of illegal robocalls.

Attestation levels: A, B, and C

The heart of the framework is the attestation level the originating carrier assigns. It reflects how confident the carrier is that the caller is legitimately entitled to use the number:

• Full attestation (A): The carrier knows the customer and confirms they are authorized to use the calling number. This is the strongest signal.
• Partial attestation (B): The carrier knows the customer but cannot confirm they are authorized to use that specific number.
• Gateway attestation (C): The carrier can only vouch for where the call entered the network — for example, a call arriving from another network. This is the weakest signal.

Higher attestation makes your calls more likely to be treated as trustworthy. Lower attestation makes them more likely to be labeled or filtered.

Why it matters for outreach teams

STIR/SHAKEN is not a law you personally file paperwork for — it operates at the carrier and network level. But it shapes your results in concrete ways:

• Answer rates. Calls with strong attestation and a clean number reputation are less likely to display spam warnings, so more of them get picked up.
• Number reputation. Analytics engines and carriers watch calling patterns. High volume, short-duration calls, and complaints can degrade a number's reputation regardless of attestation, causing "Spam Likely" labels.
• Your caller ID data. Making sure the numbers you call from are properly registered to your business — and used consistently — helps you earn and keep high attestation.

In short, STIR/SHAKEN rewards callers who are who they say they are and behave legitimately, and it penalizes spoofing and spam-like patterns.

Practical steps

• Use numbers registered to your business and make sure your calling platform and carrier can attest to them at the highest level.
• Keep calling behavior clean. Reasonable volume, real conversations, and honoring opt-outs protect number reputation.
• Register your brand where applicable. Programs exist to associate verified business identity and even branded call display with your numbers; ask your provider what is available.
• Monitor for spam labeling and remediate flagged numbers rather than just burning through new ones, which can look evasive.

How Fivra fits

Fivra's power dialer is the outbound calling surface, and Fivra's compliance layer — DNC screening before contacts are called, automatic opt-out suppression, and exportable audit logs — supports the clean, consent-based calling behavior that protects your number reputation over time. The attestation itself is assigned by carriers in the network; Fivra helps you operate in the way that earns good treatment. This is general information, not legal or telecom-engineering advice.

FAQ

What is STIR/SHAKEN?

It is a caller ID authentication framework in which the originating carrier cryptographically signs the caller ID and the terminating carrier verifies it, making it much harder to spoof the number displayed on a recipient's phone.

What are attestation levels?

Attestation reflects how confident the originating carrier is in the caller's right to use the number: A (full — customer and number verified), B (partial — customer known, number not confirmed), and C (gateway — only the entry point is vouched for). Higher is more trusted.

Will STIR/SHAKEN stop my legitimate calls from being marked as spam?

Not by itself, but strong attestation helps. Calls with full attestation and a clean number reputation are less likely to show spam warnings. Poor calling behavior can still get a number labeled regardless of attestation.

Do I have to do anything to comply with STIR/SHAKEN?

The framework operates at the carrier and network level, not through paperwork you file per call. Your job is to call from numbers properly registered to your business and to keep calling behavior clean so you earn high attestation and good reputation.

Why are my calls showing "Spam Likely"?

Common causes include low attestation, high-volume or short-duration calling patterns, complaints, or an unregistered number. Analytics engines and carriers combine these signals, so remediating reputation is usually better than constantly switching numbers.

How does Fivra help with call reputation?

Fivra's power dialer plus its compliance controls — DNC screening, automatic opt-out suppression, and exportable audit logs — support the consent-based, clean calling behavior that protects number reputation. Attestation itself is assigned by carriers; this is general information, not telecom or legal advice.