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DNCLCC Disposition for SIP 603 and 603+

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Julianne Skinner
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Overview

DNCLCC (Do Not Call Lead Consent Concern) is a system disposition applied automatically when a carrier returns a SIP 603 or SIP 603+ response. Convoso introduced DNCLCC on June 30, 2025, and expanded it on March 25, 2026 to cover new FCC-mandated carrier signaling.

A SIP 603 or 603+ response is a network-level signal that the call was declined or blocked. It may reflect a lead consent concern, carrier spam analytics flagging the call, or other network-level filtering.

Update – March 25, 2026: U.S. voice carriers now return a SIP 603+ ("Network Block") response when a call is blocked by carrier analytics, such as spam filtering. These calls are also dispositioned as DNCLCC. If you see an increase in DNCLCC dispositions, your outbound Caller IDs may be getting flagged by carriers.

What this means

  • Calls that receive a SIP 603 or SIP 603+ response are marked as DNCLCC.
  • A single DNCLCC response does not add a number to the DNC list on its own. 
    • A number is added only after repeated DNCLCC responses: at least 2 of its last 4 attempts, including the most recent one.
  • When that threshold is met, the number is added to the DNC list based on the campaign's Check Against DNC Lists setting (global, campaign, or none).
  • Numbers added to the DNC list this way are not redialed by the dialer.

Why this change

This update supports compliance with changing carrier requirements and federal regulations concerning call consent. The Federal Communications Commission (FCC) now requires carriers to signal more clearly when a call is blocked by reasonable analytics, and Convoso has updated its call signaling to align with these requirements.

Repeatedly dialing numbers that carriers have blocked creates compliance risk and can affect call attestation and deliverability for your business. Handling DNCLCC consistently helps protect your calling reputation.

What you should do

No configuration changes are required for the March 2026 update. We recommend that you:

  • Confirm your campaigns' Check Against DNC Lists setting matches how you want DNCLCC numbers handled.
  • Ensure numbers flagged as DNCLCC are excluded from future dialing attempts, including any lists you export or re-upload.
  • Monitor your DNCLCC volume. A sudden increase may mean your outbound Caller IDs are being flagged by carriers, so review your Caller ID health and rotation.
  • Contact Support if you believe calls to valid, active leads were incorrectly marked as DNCLCC. Our carrier operations team will investigate and, if a carrier error is confirmed, reset the affected records and remove those numbers from the DNC list.

 

 

 

 

 

 

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