Building a multichannel customer communication strategy shouldn’t mean dealing with API sprawl or updating integrations. As customer demand shifts towards instant, mobile messaging – with 82% of shoppers valuing real-time delivery and account updates via SMS, RCS, and WhatsApp (eCommerce News) – developers face 2 challenges: keeping integrations simple, whilst enabling multichannel messaging and high-throughput reliability.
To deliver at scale, developers connect their CRM, or another core software into a messaging platform via messaging APIs. These interfaces streamline the connection between your existing tech stack and customer communication channels, accelerating deployment, increasing operational efficiency, and unlocking multichannel scalability, all whilst improving customer experience, with key features such as messaging scheduling, throttling, and batch sending.
When looking for a business messaging solution for mobile channels, there are two main integration options: a multichannel REST API and an SMPP Protocol. In this guide, we’ll look at how each one works, which combination is right for your requirements, and the competitive advantage both provide.
What we’ll cover:
- What is a messaging API?
- Why are organisations taking an API first approach?
- Why choose a messaging API?
- Multichannel REST API: Scalable multichannel messaging
- SMPP Protocol: High-throughput SMS volume
- Webhooks: Automated real-time event tracking
- REST & SMPP: Why the best use both
- Why use Esendex as your messaging API partner
What is a messaging API?
A messaging API is like any other API. It is a digital link that allows two software systems or applications to talk to each other, without manual intervention.
A set of programming tools enables one application to request data and actions from the other and receive an immediate response. Applied to customer communications, it is a single point of integration that connects software such as the Esendex platform to the global telecommunication network. This makes it easy to manage all communications, including sending bulk messages and tracking metrics such as open rates, via a pre-built platform.
Why are APIs important?
APIs are the hidden heroes behind enterprise operations. They’re a strategic priority for any modern and ambitious business. To maintain their competitive edge, businesses need to be able to connect theirs and their partners’ systems with zero friction for either staff or customers. Adding new channels gives customers more choice, while automation ensures that these channels work together effectively to deliver a unified experience, rather than creating complexity.
According to our research, here are three key areas where a messaging API can improve operational and commercial performance:
- Competitive advantage: Companies deploying real-time API integration strategies are 35% more likely to outperform their competitors in operational efficiency. Aspire Systems
- Speed and automation: API-driven strategies achieve automation rates of up to 80% in targeted processes (compared to 30% – 40% manually). API Conference
- Efficiency and revenue: 65% of organisations now report that their API programmes serve as direct revenue drivers. Postman
Why choose a messaging API?
A messaging API connects your existing tech stack to a messaging platform, replacing manual processes and allowing your teams to automatically trigger RCS and SMS messages to your customers. APIs increase efficiency and reduce the risk of human error due to manual handling by creating a direct, secure, and standardised connection between different applications.
REST and SMPP Protocol each have their own use cases, and can be used concurrently depending on the purpose. A good provider will offer both and make it easy for teams to choose the right one at the right time. Below is an overview of the three main API protocols, their characteristics and where you could use them.
| API Protocol | What it is | Key trait | Why |
| REST (Representational State Transfer) | A modern architectural style (set of guidelines) using HTTPS. One format, one base URL, and one API key. | Lightweight and flexible. It uses various data formats, including JSON, which is easy to read. Offers a wide range of actions, tasks and channels via API. | It is what 90% of customers will expect. Used by 90% of modern web apps and CRMs (like Salesforce) Postman. This API suite offers access to the full range of features and channels on the platform and is highly modular. |
| SMPP (Short Message Peer-Peer protocol) | Industry standard binary protocol used specifically for sending & receiving high-volume SMS messages between applications & carriers. | Specific to sending one or two-way SMS. Maintains a “persistent” (always-on) connection. Is extremely robust and can handle a high throughput of messages. | If the customer requires high-volume, time-sensitive SMS, this is the specialised “high-speed lane” for that use case. Most commonly used for OTP and Emergency Alerts where reliability and speed of delivery are essential. |
| SOAP (Simple Object Access Protocol) | A rigid, highly structured protocol using XML. | Extreme security and “rules.” It’s much heavier (slower) than REST. | You will see this mostly in Banking, Healthcare, and Government where there are many older services still in operation. |
REST API – a simple explanation
REST stands for Representational State Transfer. It is a flexible architectural style that uses standard web addresses (URLs) and secure web commands (HTTPS) to transfer information between systems. You’ll also see the term ‘RESTful APIs’. This refers to whether it follows the technical rules outlined below.
- Statelessness: The system does not store data from previous requests. All new messages sent from your application via REST must include all relevant information, such as authentication.
- Client-server separation: Your software and the messaging provider’s platform operate independently. This means the provider can upgrade their infrastructure or fix bugs without you having to amend your integration code.
- Uniform interface: Developers access the API using standard web actions, such as POST to send a message or GET to fetch a message status.
The benefits of REST for businesses
- Multi-channel capabilities: Modern REST APIs can support multiple communication channels, including SMS and RCS messaging.
- Compatibility: Integrates seamlessly with modern web applications and CRM platforms leveraging the REST architectural style that powers 90% of modern web apps and CRMs (like Salesforce) Postman. This makes it the standard expected by 9 out of 10 enterprise customers.
- Readable data formats: REST typically transmits data using JSON (JavaScript Object Notation), a lightweight format that is easy for developers to read and manage.
- Built-in security: REST APIs mandate HTTPS, creating an encrypted connection that protects customer details, such as phone numbers and authentication codes.
Why choose our multichannel REST API suite?
One of the biggest benefits of our Multichannel API suite is its multichannel scalability, allowing teams to switch between SMS and RCS messaging with a single JSON parameter update – so it’s perfect for rich media marketing campaigns, two-way customer support, and detailed delivery information. Our multichannel API suite has been built with developers in mind, with modern architecture, integration in as little as 3 hours1, and enterprise-grade security (ISO 27001 and Cyber Essentials certified supplier, with 24/7 vulnerability scanning built to OWASP guidelines) mitigating migration anxiety.
Understanding SMPP
SMPP (Short Message Peer-to-Peer) is solely for integrated SMS sending – so it’s most suited to clear and direct mass communications, rather than rich marketing messages. It is an industry-standard binary protocol built specifically for sending and receiving large volumes of text messages directly between business applications and telecommunications carriers.
SMPP maintains a persistent connection between your software and the messaging server, rather than opening a new connection for every message.
- The BIND connection: SMPP uses a process called a BIND. Your software logs in once and establishes a continuous connection to the messaging server, so the channel remains permanently open.
- High-speed binary data: SMPP uses Protocol Data Units (PDUs) – compact binary packets designed for rapid processing of bulk messages. Data is transmitted as compact binary packets, so the system processes information rapidly to transmit messages in bulk.
It can handle a high throughput of 50,000 messages per send, making it well suited to bulk sending.
The benefits of SMPP for business
- Speed and throughput: Open connection and lightweight binary data allows businesses to send millions of messages per hour without authenticating every time.
- Simultaneous two-way traffic: A persistent SMPP connection supports two-way data flow. Your application can broadcast outbound texts while simultaneously receiving inbound replies and real-time delivery receipts (DLRs).
- Highly secure: Esendex secures messages in two ways. IP whitelisting that ensures data can only be transferred if a customer provides a specific approved digital address. We also use a VPN/TLS, wrapping the entire pipeline in a protective encrypted ‘sleeve’ so nobody can tap into it and view the messages.
Why choose our SMPP Protocol?
Our robust SMPP Protocol is the foundation for heavy-duty, mission-critical SMS outreach, allowing teams to control messaging traffic, stream high-volume sends over direct connections, and receive real-time insights without performance bottlenecks. It’s the ‘fast-lane’ option for large volumes and time-sensitive messaging, such as black friday offers, emergency alerts and internal employee broadcasts.
It’s especially well suited to organisations with a high volume of monthly SMS sends, who need a secure, reliable connection that can handle sustained high throughput without dropping messages or compromising data. Although SMPP requires more development time initially, it unlocks long-term reliability with minimal maintenance, potentially offsetting the initial costs with higher returns.
Cost-per-message is typically the same whether you choose a multichannel REST API or SMPP Protocol and depends on the number you send and your plan.
Should I choose REST or SMPP Protocol?
The key differences between REST and SMPP are summarised below. Which one you choose depends on the volume and type of messages you want to send, as well as your technical resources.
- Choose REST if you are looking for a fast setup, want to communicate across multiple channels, and have standard development skills within your team. It’s modular and connects easily with industry-standard software. REST also supports multichannel communications, making it suitable for marketing campaigns on RCS where you may want to include images, videos and buttons.
- Choose SMPP when your system demands extreme speed, massive scale, and deep telecom-level control. If you only need to send SMS notifications to mobiles in large volumes as quickly as possible, usually for time-sensitive alerts, then SMPP is the right solution.
- Choose both if you’re looking to scale your customer communication across multiple channels and different departments. REST API is perfect for your customer support and marketing teams looking to engage customers with 2-way conversations and rich media messages, whilst an SMPP connection enables mass reach, high throughput and robust reliability.
With 25% of enterprise organisations operating as fully API-driven businesses (Spherical Insights), modern engineering teams rarely limit themselves to a single protocol – they deploy REST for multichannel engagement and SMPP for persistent, bulk SMS. In other words, you don’t have to choose just one.
The role of webhooks
All communications depend on being able to receive incoming data from the mobile network, whether or not you choose REST or SMPP. An API allows you to send requests to a server – but a webhook then automatically pushes information back to your application. Think of it like this:
- Standard API (the request): Business initiates an action e.g. send SMS
- Webhook (the event): Provider notifies sender that the message has been delivered
Rather than manually checking to see if a message has been sent (or other status update), JSON data is delivered directly into your CRM or database so you get an automatic notification in near real-time. This is critical for:
- Delivery receipts (DLR): Customers are notified as soon as the carrier confirms a message has been delivered.
- Two-way conversations: A text is hooked back to your CRM as soon as an end-user replies to a message.
- Opt-out compliance: Automatically updating your database when an end user texts “STOP” to unsubscribe.
- Combatting fraud: A spike in failed webhooks can trigger an alert that an account might have been compromised.
Webhooks use public URLs so the application can accept incoming data. However, these can be secured using OAuth 2.0 tokens, custom API headers, and DNS domain trust configurations.
Why use Esendex as your messaging API partner
Whether deploying REST, SMPP, or a combination of both, Esendex provides a unified, modern infrastructure that can be used by developers and those without a technical background:
- Modern architecture: Eliminate API sprawl with unified JSON schemas, single base URLs, and comprehensive documentation built for rapid deployment and multichannel scalability.
- Enterprise-grade security: ISO 27001 accredited, Cyber Essentials certified, and supported by 24/7 active vulnerability monitoring built to strict OWASP guidelines.
- Intuitive developer documentation: Access intuitive code samples, interactive 5-minute integration challenges, and local human support included as standard.
Ready to streamline your communication stack? Explore our developer documentation or start a free trial and deploy your first SMS messages via our multichannel REST API within 5 minutes2.
1 From account setup and verification to first successful API SMS send. Based on the average time taken for a new REST API Prepay customer (03/25 – 05/26)
2 Based on our fastest customer integration time from free trial sign-up to first successful SMS message sent via API and independent in house testing.
