# What is an ESME?

> ESME (External Short Messaging Entity) is the SMPP term for any application outside the SMSC that submits or receives SMS. In an A2P deployment your gateway is the ESME, binding to the operator's SMSC over SMPP. An ESME binds in one of three session modes — Transmitter (send-only), Receiver (receive-only), or Transceiver (both directions on one connection, added in SMPP 3.4). Modern deployments almost always use a single Transceiver bind.

- Canonical URL: https://www.broadnet.me/answers/what-is-esme
- Language: en
- Last reviewed: 2026-07-22
- Publisher: BroadNet (https://www.broadnet.me)

## The three bind types

Transmitter (TX) submits messages only; Receiver (RX) accepts delivery receipts and inbound MO only; Transceiver (TRX) does both over one socket and is the default today. Whatever the mode, the ESME keeps the session alive with periodic enquire_link heartbeats and reconnects with backoff on failure. See /answers/what-is-smpp and /answers/smpp-3-4-vs-5-0.

## ESME vs SMSC

The ESME is the client; the SMSC is the operator-side server that stores and forwards the message to the handset. The SMSC returns a message_id on submit and later streams the DLR back over the same bind. When a bind or submit fails, the SMSC returns an SMPP command_status you can decode with the /tools/smpp-error-codes lookup. See /answers/what-is-smsc and /answers/what-is-dlr.

## Related

- [All answers](https://www.broadnet.me/answers)
- [Glossary](https://www.broadnet.me/answers)
- [What is SMPP?](https://www.broadnet.me/answers/what-is-smpp)
- [How does the SMPP protocol work?](https://www.broadnet.me/answers/smpp-protocol)
- [SMPP 3.4 vs SMPP 5.0 — what changed and what to use](https://www.broadnet.me/answers/smpp-3-4-vs-5-0)
- [What is an SMSC?](https://www.broadnet.me/answers/what-is-smsc)
- [What is a DLR (Delivery Receipt)?](https://www.broadnet.me/answers/what-is-dlr)
- [SMPP integration](https://www.broadnet.me/developers/smpp)
- [SMPP error-code lookup](https://www.broadnet.me/tools/smpp-error-codes)
- [SMS API](https://www.broadnet.me/products/sms-api)