Glossary

The telecom and verification terms behind our checks, explained with sources.

10DLC: 10DLC is US business text messaging sent from ordinary 10-digit phone numbers, registered by brand and campaign. How registration works and why it affects delivery.
A2P SMS: A2P SMS is text messaging sent by software on behalf of a business, such as one-time passcodes, alerts and reminders. How it differs from P2P and how it is regulated.
Caller ID name (CNAM): CNAM is the caller name shown with incoming calls in North America, looked up by the called party's carrier. How it works, why it is often wrong, and what we don't do.
Catch-all e-mail address: A catch-all (accept-all) domain accepts mail for any address at that domain, so no check can prove a specific mailbox exists. What it means and how to treat it.
Delivery receipt (DLR): A delivery receipt (DLR) is the status report a network returns after an SMS is delivered or fails. What DLR statuses mean and why a missing receipt isn't proof of failure.
Disposable e-mail address: A disposable e-mail address is a temporary or throwaway inbox used to avoid giving a real address. How it works, how it differs from privacy relays, and how to handle it.
E-mail bounce (hard vs soft): An e-mail bounce is a message returned as undeliverable. Hard bounces are permanent, soft bounces temporary. How to read bounce codes and keep your bounce rate low.
E.164 phone number format: E.164 is the international phone number format: a plus sign, a country code and up to 15 digits in total. Why APIs use it and how to convert to it.
HLR lookup: An HLR lookup queries a mobile number's home network to find out whether the number is live, ported or roaming. How it works and what it can't tell you.
International mobile subscriber identity (IMSI): The IMSI is the permanent identifier of a mobile subscription, stored on the SIM. How it differs from the phone number and why MobileValidate never returns it.
International revenue share fraud (IRSF): IRSF pushes calls or texts to high-cost international numbers so the fraudster earns part of the fee. Warning signs, IRSF number databases and defences.
Local routing number (LRN): An LRN is the 10-digit number US and Canadian networks use to route calls and texts to a ported phone number. How LRN routing works and why prefix-based carrier lookups get it wrong.
MCC and MNC codes: MCC and MNC codes identify a mobile network: a 3-digit country code plus a 2- or 3-digit network code, defined by ITU-T E.212. How to read them.
Mobile number portability (MNP): Mobile number portability lets subscribers keep their number when they switch networks. Why it breaks prefix-based carrier detection and how to handle it.
Mobile virtual network operator (MVNO): An MVNO is a mobile operator that sells service under its own brand on another operator's radio network. Why carrier lookups name MVNOs, and what it means for SMS and fraud checks.
Model Context Protocol (MCP): The Model Context Protocol (MCP) is an open standard for connecting AI applications to external tools and data. How MCP servers, tools and transports work, and what the 2026-07-28 spec changed.
MSISDN: An MSISDN is the full international phone number of a mobile subscription: country code, network code and subscriber number. How it differs from the IMSI.
MX record: An MX record is the DNS entry that names the mail servers accepting e-mail for a domain. How MX lookups work, what null MX means, and what an MX check can't tell you.
Number reachability: A valid number has the right format; a reachable number is live on a network right now. Four levels of phone number checks and what each tells you.
Number Verification API: CAMARA Number Verification asks the operator if the number a user typed belongs to the SIM in their device. How it works, who offers it in 2026, limits.
One-time password (OTP): A one-time password (OTP) is a short code valid for a single sign-in or action. How SMS, WhatsApp, voice and app OTPs work, their weaknesses, and how to protect OTP flows.
Passkey: A passkey is a phishing-resistant sign-in credential based on public-key cryptography (FIDO/WebAuthn). How passkeys work, passkey vs OTP, and why phone numbers still matter.
Phone number line type: Line type is the kind of service a number belongs to: mobile, fixed line, VoIP, toll-free, premium rate and more. What each means for SMS and calls.
Rich Communication Services (RCS): RCS is the carrier messaging standard that adds rich media, read receipts and verified business messages to the phone's built-in messaging app. How it differs from SMS.
Sender ID: A sender ID is the name or number shown as the sender of an SMS. Alphanumeric, long-code and short-code sender IDs, national registries, and why sender IDs affect delivery.
Signalling System No. 7 (SS7): SS7 is the signalling protocol suite that phone networks use to set up calls, route SMS and support roaming. Why its trust model creates security risks for SMS codes.
SIM swap: A SIM swap moves a phone number to a new SIM. In SIM swap fraud, a criminal does it to receive the victim's calls and one-time passcodes. How it works and how to defend.
Smishing: Smishing is phishing by text message: a fraudulent SMS that lures people into clicking a link, sharing a code or calling a number. How it works, the numbers, and how businesses reduce it.
SMS pumping: SMS pumping is fraud in which bots trigger OTP or sign-up texts to numbers that earn the attacker a share of the fees. How it works and how to reduce it.
STIR/SHAKEN: STIR/SHAKEN is the caller ID authentication framework used in US and Canadian phone networks. How attestation levels A, B and C work and what they don't tell you.
VoIP number: A VoIP number is served over the internet, not a mobile or fixed network. Why it matters for OTP and fraud checks, and why it is not a red flag alone.
Wangiri: Wangiri is a phone scam: a call rings once from a high-cost international number to trick people into calling back. How it works and how businesses avoid paying for it.