# What is A2P SMS? Business messaging

A2P SMS starts in an application and ends on a person's handset. P2P SMS starts on a handset. The same network can carry both; what differs is the sender registration, the business route and the delivery receipt that travels back.

- A2P messages start in an application; P2P messages start on a handset.

- A delivery receipt reports a network state, not that a person read the message.

- Authentication, transactional and promotional traffic carry different rules.

- Gray routes that disguise A2P as P2P are outside our traffic policy.

## Two kinds, one network

A bank sends a login code. A courier sends a delivery window. A retailer sends an opted-in offer. Each message starts in an application, so each is A2P: application-to-person. A person texting a friend is P2P: person-to-person. The handset, the radio network and often the same message center carry both. The difference is who starts the message and what the network knows about the sender.
That difference changes the treatment. A2P traffic runs on a registered sender and a business route. P2P runs on a consumer subscription. The same words can be A2P from a bank and P2P from a friend, and the network should treat them differently.

## The receipt is a network status

A delivery receipt, or DLR, reports what the network did with a submitted message. It may say delivered, expired, undelivered or unknown, with a code that explains the state. It does not say that a person opened the message, read the code or acted on it. A handset that is off, full or out of coverage produces a different state from a handset that received the message and ignored it.
Read the DLR as one signal in the funnel. Pair it with your own events: code entered, order completed, reply received. A high delivery rate with a low completion rate points to the message, the sender or the form, not to the network alone.

### Where an A2P message goes

The application submits to a gateway; the message center looks up the subscriber; the receipt returns on the same chain.

Alt: A seven-step path from application to SMPP gateway, message center, home location register, serving switch, handset and delivery receipt.

The application connects over SMPP or HTTP to a gateway. The gateway passes the message to the short message service center. The center asks the home location register or HSS where the subscriber is registered, then hands the message to the serving mobile switching center or mobility management entity. The handset acknowledges receipt, and the delivery receipt travels back through the same chain. Each hop can delay, filter or rewrite the message.

| Item | Value | Note |
| --- | --- | --- |
| First state · 1 | Application |  |
| First state · 2 | SMPP gateway |  |
| First state · 3 | SMSC |  |
| First state · 4 | HLR / HSS |  |
| First state · 5 | MSC / MME |  |
| First state · 6 | Handset |  |
| First state · 7 | Delivery receipt |  |

Source: 3GPP TS 23.040: Technical realization of the Short Message Service (https://www.3gpp.org/ftp/Specs/archive/23_series/23.040/)

## Three traffic types, three sets of rules

Authentication traffic carries one-time passwords, login approvals and verification codes. It is small, time-sensitive and valuable to an attacker. Transactional traffic carries alerts, receipts and appointment reminders. Promotional traffic carries marketing and re-engagement messages, and it needs a recorded opt-in and a working opt-out.
Keep the three apart. A marketing burst on the same route can delay a login code. An authentication route sized for short codes may not match a campaign that needs a high sustained rate. Each type also meets its own content filters, so a template that passes for one can fail for another.

A2P is just bulk P2P. The messages look the same, so the network treats them the same.
The text may be identical. The origin, the registered sender and the route are not. A2P runs on a business path with sender registration and receipts; P2P runs on a consumer subscription. Disguising A2P as P2P to avoid that path is gray routing, which our traffic policy excludes.

## What buyers check

Ask which sender types work in each destination and what registration each needs. Ask which routes carry your traffic and whether the provider tells you before a route changes. Ask what a delivery receipt means and whether the provider tests handsets in the markets you care about. Ask how content is screened and how opt-outs are handled.
Ask for a test route with your own content and sender before launch. Ask what data the provider keeps and for how long. Ask what happens when a route fails or a sender is rejected. Ask who tells you when a route changes and how much notice you get. The [SMPP explainer](/en/resources/learn/what-is-smpp/) covers the connection; the [sender ID guide](/en/resources/learn/sender-id-mx-br/) covers registration in Mexico and Brazil.
Put the answers in one table: destination, sender type, registration owner, route, test date and fallback. A table with gaps is more useful than a polished deck, because it shows which question the provider did not answer. Score the evidence, not the relationship.

The count updates in the browser; the text stays there.

[Open the tool](/en/tools/sms-segments/?src=learn-what-is-a2p-sms&scenario=otp-unicode&text=Your+code+is+123456.+It+expires+in+10+minutes.)

## P2P, P2A and two-way

A2P describes the outbound direction: application to person. P2A describes the reverse: a person replies to the application, and the reply reaches a callback or an inbox. A two-way program uses both. The reply path needs a sender that can receive messages, usually a short code or a long number, and a route that carries mobile-originated traffic. An alphanumeric sender usually cannot receive replies, which is why two-way programs choose a number.
P2P remains person-to-person and is not a business channel. A business that asks customers to text a personal number creates a P2P flow with business consequences: no sender registration, no delivery report to the business and no control over the route. If the program needs accountability, use an A2P sender with a two-way path.

### Check what you learned

**A message shows delivered, but the user says no code arrived. What do you check first?**

Check the handset state, the sender and the route. A delivered receipt means the network accepted the message, not that the handset displayed it.

**Why can a marketing burst slow an OTP?**

Both share a route and a throughput allocation. A burst fills the window, so the code waits. Separate the traffic or size the route for the peak.

**Which sender type carries replies?**

A short code or a long number. An alphanumeric sender is one-way in most networks.

## FAQ

**Is OTP A2P?**

Yes. One-time passwords are the canonical A2P use, alongside transaction alerts and consented marketing.

**Is A2P only marketing?**

No. Most A2P traffic is authentication and transactional. Marketing is a subset and needs a recorded opt-in.

**What is a gray route?**

A route that disguises A2P traffic as P2P or otherwise bypasses the registered business path. It is outside our traffic policy because it avoids the controls that protect delivery and sender identity.

**Why do sender IDs change between countries?**

Each market has its own sender rules and registration. A sender that is valid in one country may be rewritten, blocked or rejected in another.

**Do I need opt-in?**

Marketing needs a recorded opt-in, and the consent basis for transactional messages depends on the market. Take legal advice on your obligations.

## Sources

- [3GPP TS 23.040: Technical realization of the Short Message Service (SMS)](https://www.3gpp.org/ftp/Specs/archive/23_series/23.040/) — Accessed: 2026-10-19
- [3GPP TS 23.038: Alphabets and language-specific information](https://www.3gpp.org/ftp/Specs/archive/23_series/23.038/) — Accessed: 2026-10-19
- [3GPP TS 23.003: Numbering, addressing and identification](https://www.3gpp.org/ftp/Specs/archive/23_series/23.003/) — Accessed: 2026-10-19
- [SMPP delivery receipts: states and receipt fields](https://smpp.org/smpp-delivery-receipt.html) — Accessed: 2026-10-19

Updated: 2026-10-19