The Three-Layer Problem Most Teams Get Wrong
Most compliance checklists treat contact suppression as a single checkbox: are we honoring opt-outs? In practice, there are three entirely separate failure modes, each caught by a different mechanism, and each one invisible to the other two.
Skipping any layer leaves a gap. Skipping the litigator scrub specifically leaves a gap that can result in coordinated TCPA litigation — because some people on your list are not accidentally there; they placed themselves there on purpose.
Here is how each layer works, what it misses, and how to wire all three into a real campaign pipeline.
Layer 1: The Federal Do-Not-Call Registry
The National Do-Not-Call Registry, maintained by the FTC, lets consumers register their phone numbers to opt out of unsolicited telemarketing calls. Businesses making outbound calls for marketing purposes are legally required to scrub against it at least every 31 days.
What it catches: Consumers who proactively told the government they do not want telemarketing calls.
What it misses: Numbers registered after your last scrub window. Numbers that were never registered. Numbers belonging to serial litigants who registered specifically to collect evidence — registration alone does not signal intent. And critically, it covers calls; SMS compliance rules under the TCPA and state laws operate on a separate track.
Practical note: DNC registration is a floor, not a ceiling. Regulators and courts have made clear that a valid DNC scrub does not immunize you from TCPA claims based on consent failures, calling abandoned or reassigned lines, or contacting known litigators.
Layer 2: Your Internal Opt-Out List
Every outbound program should maintain its own suppression list — numbers where a contact has asked you, specifically, not to call or text them again. This list is yours to build and yours to honor, regardless of DNC status.
What it catches: Prior customers or leads who revoked consent, numbers that generated complaints internally, and any contact who used your opt-out mechanism (reply STOP, verbal request, web form).
What it misses: People who never contacted you before. Reassigned numbers — a number that opted out two years ago may belong to a completely different person today. And litigants who have not yet interacted with your brand.
Before calling a number that has been sitting in your CRM for more than a few months, it is worth verifying whether it is still active and still belongs to the same person. CheckThatPhone returns a deactivationDate field when a number has been deactivated, and the deliverable flag tells you whether the number is currently reachable at all. If a number on your internal suppression list shows a recent deactivationDate, it may have been reassigned — which creates a separate risk: you could be calling a stranger who never opted out of anything.
The /v1/lookup endpoint also returns blackList, action, and reason fields. If blackList is true, the number is flagged in CheckThatPhone’s own risk database, and action will tell you what to do with it (typically suppress or review).
Layer 3: The TCPA Litigator Scrub
This is the layer most teams skip, and it is the one with the most asymmetric downside.
A small but well-documented group of individuals — sometimes called serial TCPA plaintiffs or professional litigants — deliberately provide their phone numbers to businesses, wait for contact, and then file or threaten TCPA lawsuits. They are not on the DNC registry by accident. They are not on your internal opt-out list at all. From your data’s perspective, they look like any other lead.
The litigator scrub is a lookup against a database of phone numbers associated with known TCPA litigants and their attorneys. It does not protect you from every claim, but it removes the low-hanging fruit: numbers that have a documented history of litigation activity.
With CheckThatPhone, you enable this by adding litigatorFilter: true to your lookup request:
POST https://api.checkthatphone.com/v1/lookup
Authorization: Bearer <key>
Content-Type: application/json
{
"phone": "2025550178",
"litigatorFilter": true
}The response includes three fields:
litigator— boolean, true if the number is flaggedlitigator_type— categorizes the match (e.g., plaintiff, attorney)litigator_name— the name associated with the record where available
If litigator is true, suppress the number before it ever enters your dialer queue. Do not call it. Do not text it. The potential cost of one TCPA claim — statutory damages range from $500 to $1,500 per violation, and violations can be counted per message — far exceeds the value of any single contact.
For more on how this fits into a broader TCPA risk strategy, see our TCPA litigator scrub use case.
Layering All Three in a Real Campaign Pipeline
Here is a concrete sequence for an outbound SMS or calling campaign:
Step 1 — Line type and carrier validation
Before anything else, confirm you know what kind of number you are dialing. CheckThatPhone returns nanpType (mobile, landline, not-mobile) and carrier details via dipCarrier, dipCarrierType, dipCarrierSubType, and dipPorted. A ported number that has moved from a landline carrier to a mobile carrier is now subject to TCPA’s autodialer restrictions even if you originally captured it as a landline. Missing this is a common source of consent failures.
If you need to reach landline numbers via SMS through registered messaging services, you can add landlineSmsLookup: true to the request — the response will include dipMessagingLookup, dipMessagingEnabled, and dipMessagingProvider to tell you whether that specific landline can receive messages.
Step 2 — Deliverability and blacklist check
Check deliverable, blackList, action, and reason. Remove numbers that are not deliverable or are flagged. If deactivationDate is present and recent, treat the number as potentially reassigned — do not rely on historical consent.
Step 3 — Litigator scrub
Run litigatorFilter: true. If litigator returns true, suppress immediately. Log the litigator_type and litigator_name for your compliance records.
Step 4 — DNC registry scrub
Apply your most recent DNC scrub file. This should happen at least monthly; more frequently if your list turns over fast.
Step 5 — Internal opt-out suppression
Cross-reference your internal list last, since it is the most current signal about your specific relationship with that contact.
Only numbers that clear all five checks should enter the active campaign.
Running This at Scale
For real-time lead qualification — a web form submission, an inbound call, a new CRM record — the single-number endpoint at POST https://api.checkthatphone.com/v1/lookup handles per-request checks with low latency.
For existing lists of thousands or hundreds of thousands of numbers, use the Bulk CSV feature in the dashboard (Dashboard → Bulk CSV). Upload your file, select the add-ons you need (including litigator filter and landline SMS lookup), and download the enriched results. The service deduplicates rows, validates carrier and line type, and runs every add-on you have enabled for each number. Uploaded files and result files are deleted within 24 hours of delivery. This is the right path for pre-campaign list hygiene — not looping the API endpoint once per number at scale.
See /pricing for add-on costs and volume tiers, and /docs for full field reference and request schema.
The Bottom Line
Each suppression layer is designed to catch a specific failure mode. The DNC registry catches consumers who opted out federally. Your internal list catches people who opted out of your program specifically. The litigator scrub catches people who never intended to opt out — because they want you to call them.
Running only one or two of these layers does not give you partial protection. It gives you a gap that motivated parties know how to find.
If your current pipeline does not include all three, contact list hygiene and sales lead validation are good starting points for understanding where these checks fit in practice.