Last Updated: September 22nd, 2025
Overview
Telephone service providers (also referred to as "carriers") evaluate every call that traverses their network to determine the likelihood that a call is legitimate and the caller ID hasn't been spoofed. This process is called call attestation. This guide will provide an overview of call attestation and what to do if your calls have been marked as "Spam Likely".
Call Attestation
Attestation is a way for a voice service provider to indicate how confident they are that a call is legitimate and that the caller ID hasn't been spoofed.
There are three levels of attestation:
Full Attestation (A)
- Definition: The provider fully verifies the caller's identity and confirms they are authorized to use the calling number.
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Requirements:
- The provider has a direct relationship with the caller.
- The caller is using a number assigned to them.
- Impact: Highest trust level. These calls are least likely to be flagged as spam.
- Example: A business using its own registered number through its carrier.
Partial Attestation (B)
- Definition: The provider knows the caller but cannot verify that they are authorized to use the specific caller ID.
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Requirements:
- The provider has a relationship with the caller.
- The caller ID may be valid, but the provider can't confirm ownership.
- Impact: Medium trust level. These calls may be flagged as “spam likely” depending on other factors.
- Example: A reseller or third-party using a number not directly assigned to them.
Gateway Attestation (C)
- Definition: The provider cannot verify the caller or the caller ID.
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Requirements:
- The call is received from an international gateway or unknown source.
- Impact: Lowest trust level. These calls are most likely to be flagged or blocked.
- Example: Calls coming from outside the U.S. or from unknown networks.
Other Impacts on Call Attestation
Call attestation is one factor in whether calls are labeled "spam likely". If you would like to see what other factors contribute to calls being labeled as "spam likely", please see our guide, Key Factors That Lead to Spam Likely Labeling