Telecom Glossary for Phone, SMS and Email

10DLC Messaging and A2P 10DLC (10-digit long code) is the US system for A2P SMS over standard local numbers.

A2P messaging Messaging and A2P A2P (application-to-person) messaging is SMS sent by software to a mobile user.

Catch-all domain Email deliverability A catch-all domain accepts email for every address at the domain. Country calling code Numbers and formats A country calling code is the one-to-three-digit prefix for a country or shared zone. CPaaS Messaging and A2P CPaaS (Communications Platform as a Service) sells SMS, voice and messaging as cloud APIs.

Delivery receipt Messaging and A2P A delivery receipt (DLR) is the status report an operator returns for each SMS. Disposable email address Email deliverability A disposable email address comes from a service issuing short-lived inboxes. DKIM Email deliverability DKIM (DomainKeys Identified Mail) signs each outgoing email. DMARC Email deliverability DMARC is a DNS policy for mail failing SPF and DKIM alignment. Donor network Networks, HLR and porting The donor network is the operator a phone number ports away from.

E.164 Numbers and formats E.164 is the ITU-T standard for international phone numbers. eHLR Networks, HLR and porting eHLR is ScoreMachine's own check on whether a number is in use.

Grey route Messaging and A2P A grey route delivers A2P SMS through a channel priced for person-to-person traffic. GSM-7 Messaging and A2P GSM-7 is the default 7-bit SMS alphabet.

Hard bounce Email deliverability A hard bounce is a permanent email delivery failure. HLR Networks, HLR and porting The HLR (Home Location Register) is the subscriber database in a mobile operator's core network. HSS Networks, HLR and porting The HSS (Home Subscriber Server) is the 4G LTE and IMS successor to the HLR.

IMSI Networks, HLR and porting The IMSI (International Mobile Subscriber Identity) is the up-to-15-digit code on a SIM. International prefix Numbers and formats An international prefix is the code dialed to leave the home country's network.

Line type Numbers and formats Line type is the kind of service behind a phone number: mobile, landline or VoIP.

MAP Networks, HLR and porting MAP (Mobile Application Part) is the SS7 layer for mobile network functions. MCC and MNC Networks, HLR and porting The MCC (mobile country code) names a country in three digits. MNO Networks, HLR and porting An MNO (mobile network operator) runs its own radio network under a spectrum license. MNP Networks, HLR and porting MNP (mobile number portability) lets a subscriber keep a phone number when switching operators. MSISDN Numbers and formats MSISDN stands for Mobile Station International Subscriber Directory Number. MVNO Networks, HLR and porting An MVNO (mobile virtual network operator) sells mobile service on another operator's radio network. MX record Email deliverability An MX (mail exchanger) record is the DNS entry naming a domain's mail servers.

National destination code Numbers and formats The national destination code (NDC) follows the country calling code. Numbering plan Numbers and formats A numbering plan is the national rulebook for phone numbers. Numbering range Numbers and formats A numbering range is a block of consecutive numbers allocated to one operator.

OTT messaging Messaging and A2P OTT (over-the-top) messaging runs over the internet instead of the operator's SMS network.

P2P messaging Messaging and A2P P2P (person-to-person) messaging is SMS sent from one handset to another by a person. Ported number Networks, HLR and porting A ported number has moved from one operator to another under mobile number portability.

Range holder Numbers and formats The range holder is the operator allocated a numbering range. RCS Messaging and A2P RCS (Rich Communication Services) is the GSMA standard adding images, buttons and verified senders to SMS. Reachability score Numbers and formats A reachability score ranks how reachable a phone number is. Recipient network Networks, HLR and porting The recipient network is the operator a phone number ports to. Role-based email address Email deliverability A role-based email address belongs to a function instead of a named mailbox holder.

Sender ID Messaging and A2P A sender ID is the name or number shown as the sender of an SMS. Sender reputation Email deliverability Sender reputation is the standing mailbox providers give a sending domain and IP. Serving network Networks, HLR and porting The serving network is the operator holding a phone number's subscription today. Short code Messaging and A2P A short code is a shortened number for high-volume A2P SMS. SMPP Messaging and A2P SMPP (Short Message Peer-to-Peer) is the open protocol linking an SMSC to external systems over TCP/IP. SMS Messaging and A2P SMS (Short Message Service) is the text messaging service built into mobile networks. SMS aggregator Messaging and A2P An SMS aggregator connects to a large set of operators and resells SMS routes. SMS gateway Messaging and A2P An SMS gateway connects software to mobile networks for sending and receiving SMS. SMS segment Messaging and A2P An SMS segment is one part of a message split across two or more SMS. SMSC Messaging and A2P An SMSC (Short Message Service Center) stores and forwards SMS. SMTP Email deliverability SMTP (Simple Mail Transfer Protocol) is how mail servers send email to each other. SMTP status codes Email deliverability SMTP status codes are three-digit mail server replies. Soft bounce Email deliverability A soft bounce is a temporary email delivery failure. Spam trap Email deliverability A spam trap is an address blocklists and mailbox providers run to catch poor list hygiene. SPF Email deliverability SPF (Sender Policy Framework) is a DNS TXT record listing a domain's permitted sending servers. SRI-SM Networks, HLR and porting SRI-SM (Send Routing Info for Short Message) is the MAP query an SMSC sends the HLR. SS7 Networks, HLR and porting SS7 (Signaling System No. 7) carries call setup, SMS routing and subscriber queries between networks. Subscriber number Numbers and formats The subscriber number (SN) is the last part of a phone number, after the NDC.

Toll-free number Numbers and formats A toll-free number is paid for by the called party, so the caller pays nothing. Trunk prefix Numbers and formats A trunk prefix is the digit dialed before a national number on a domestic call.

UCS-2 Messaging and A2P UCS-2 is the 16-bit SMS encoding for characters outside GSM-7.

VLR Networks, HLR and porting The VLR (Visitor Location Register) is a temporary database attached to a mobile switching center. VoIP number Numbers and formats A VoIP number runs over an internet connection, not a copper line or a mobile network.